Reproduction and genetic variation

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レッスンノート

Types of Reproduction

All living organisms must reproduce so their species does not become extinct.
There are two basic types: asexual reproduction (one parent) and sexual reproduction (two parents).
Asexual reproduction produces offspring identical to the parent; no mating is needed.
Sexual reproduction combines genetic material (DNA) from two parents, producing genetically unique offspring.
Examples of asexual reproducers: bacteria, protists, some insects, fish, reptiles.
Some species can switch between asexual and sexual reproduction (e.g., aphids) – called heterogamy.

Asexual Reproduction

Offspring arise from a single parent and have the exact same genetic material as the parent.
Advantage: quick and easy; no need to find a mate.
Disadvantage: no genetic variation; offspring inherit any harmful genes from the parent.
Examples: bacteria (binary fission), flatworms (fragmentation), some insects/fish/lizards (parthenogenesis).
In parthenogenesis, an unfertilized egg grows into a new organism; common in honeybees (drones).

A mother aphid with offspring, produced asexually or sexually depending on conditions.

Sexual Reproduction

Involves two parents; male produces sperm, female produces eggs.
Fertilization occurs when sperm and egg fuse to form a zygote – the first cell of a new organism.
Offspring are genetically unique because they inherit a mix of traits from both parents.
Sex cells (gametes) have half the genetic material of body cells; in humans, 23 chromosomes each.
In plants, sperm is in pollen, egg is in the ovary of the flower; fertilization leads to seed formation.

During sexual reproduction, a sperm fertilizes an egg.

Reproduction in Angiosperms (Flowering Plants)

Flowers are the sexual organs of angiosperms; they produce male and female structures.
Sexual reproduction in angiosperms results in the formation of seeds.
Pollination is the transfer of pollen from the male part to the female part; often aided by pollinators like bees and butterflies.
After fertilization, the egg grows into an embryo inside a seed; the seed can germinate into a new plant.
Seeds are often contained in fruits which help in seed dispersal.

Butterflies receive nectar when they deposit pollen into flowers, resulting in cross-pollination.

Genetic Material and Inheritance

Heredity is the passing of traits from parents to offspring; genetics is the study of this process.
Traits are coded by genes, which are sections of chromosomes located in the cell nucleus.
Chromosomes and genes are made of DNA, which acts as a blueprint for building proteins.
Changes in DNA sequence account for differences in traits among species.
Inheritance is how traits are passed down from generation to generation.

DNA, genes and chromosomes: genes are sections of chromosomes, and chromosomes are made of DNA.

Variation

Variation refers to the differences between individuals within the same species.
Variation arises from sexual reproduction, as offspring inherit a mix of traits from both parents.
All humans belong to the species×Homo sapiens×, yet there is huge variation in traits like height, skin color, and hair type.
Variation is important because it allows species to adapt to changing environments.
Examples of inherited human traits: tongue rolling, earlobe attachment, dimples, thumb shape.

Different breeds of dogs showing variation within a species.

Natural Selection

Natural selection is the process where individuals better adapted to their environment survive and reproduce more successfully.
These advantageous traits are passed on to offspring, increasing their frequency in the population over generations.
The peppered moth example: during the Industrial Revolution, dark-colored moths became more common because they were camouflaged on soot-covered trees.
Natural selection leads to adaptation of species over time.
Small changes can occur within a few generations, but major changes take thousands of years.

A bird preying on peppered moths on light lichen-covered bark and on soot-darkened bark, illustrating natural selection.

Punnett Squares and Genetic Prediction

A Punnett square is a tool used to predict the possible genotypes of offspring from a cross between two parents.
It is based on probability and shows the combination of alleles from each parent.
Example: crossing two purple pea plants (Bb x Bb) yields 25% white flowers (bb) and 75% purple (BB or Bb).
Punnett squares are not used for asexual reproduction because offspring are genetically identical to the single parent.

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練習問題

無料プレビュー — 48問中8問。すべて見るには登録を。

1.Asexual reproduction requires two parents.
Easy
True or false?
2.In sexual reproduction, the offspring are:
Easy
- AIdentical to one parent
- BIdentical to both parents
- CSimilar but not identical to the parents
- DAlways different from both parents
3.In humans, sex cells contain 46 chromosomes.
Easy
True or false?
4.Which of the following is an advantage of asexual reproduction?
Easy
- AIt produces genetically diverse offspring
- BIt does not require finding a mate
- CIt results in offspring with traits from both parents
- DIt always produces more offspring than sexual reproduction
5.In angiosperms, where is the egg contained?
Medium
- AIn the pollen
- BIn the ovary
- CIn the petal
- DIn the sepal
6.In asexual reproduction, offspring are genetically identical to the parent.
Medium
True or false?
7.Which of the following organisms can reproduce both asexually and sexually?
Medium
- ABacteria
- BAphids
- CHumans
- DYeast
8.Which of the following are types of asexual reproduction? (select all that apply)
Medium
- ABinary fission
- BFragmentation
- CParthenogenesis
- DFertilization
- EPollination

もっと問題

9.In sexual reproduction, offspring are genetically identical to their parents.
Medium
True or false?
10.Match the term with its description.
Medium
- Gene
- Chromosome
- DNA
- Contains codes for traits
- Structure in nucleus that carries genes
- Blueprint for living organisms
11.What did the light-coloured moths originally blend in with?
Medium
- ADark soot-covered trees
- BLight-coloured trees and lichens
- CGreen leaves
- DGrey rocks
12.After the Industrial Revolution, why did the number of dark-coloured moths increase?
Medium
- AThey were better camouflaged on soot-covered trees
- BThey were stronger and faster
- CThey produced more offspring
- DThey could eat more
13.Which of the following best describes the difference between a species and a breed?
Medium
- ASpecies can interbreed to produce fertile offspring, while breeds are variations within a species
- BSpecies are always larger than breeds
- CBreeds can interbreed with other breeds, but species cannot
- DThere is no difference
14.Why are Punnett squares not used to model asexual reproduction?
Hard
- ABecause there is only one parent, so all offspring are identical
- BBecause asexual reproduction does not involve genes
- CBecause Punnett squares only work for plants
- DBecause asexual reproduction is too fast
15.In a Punnett square for a cross between two Bb parents, what is the genotype ratio?
Medium
- A1 BB : 2 Bb : 1 bb
- B2 BB : 2 Bb : 0 bb
- C3 BB : 1 Bb : 0 bb
- D1 BB : 1 Bb : 2 bb
16.In sexual reproduction, the offspring receive half of their genetic material from each parent.
Medium
True or false?
17.Which of the following is NOT a method of asexual reproduction?
Easy
- ABinary fission
- BBudding
- CParthenogenesis
- DFertilization
18.In flowering plants, the sperm is contained in the pollen.
Medium
True or false?
19.What is the function of a pollinator?
Medium
- ATo transfer pollen from one flower to another
- BTo produce seeds
- CTo provide nutrients to the plant
- DTo protect the flower
20.In the peppered moth example, what caused the change in the population's colour?
Medium
- ANatural selection due to pollution
- BThe moths changed colour to match trees
- CThe moths ate different food
- DThe moths migrated to different areas
21.All bacteria reproduce sexually.
Easy
True or false?
22.Which of the following statements about variation is correct?
Hard
- AVariation only occurs in animals
- BVariation is the difference between individuals of the same species
- CVariation is always inherited from parents
- DVariation is caused by environmental factors only
23.Put the following steps of seed formation in angiosperms in order:
Medium
- Pollination
- Fertilization
- Seed formation
- Germination
24.Which of the following are examples of inherited traits? (select all that apply)
Medium
- ATongue rolling
- BHeight
- CLanguage spoken
- DSkin colour
25.In the Punnett square for a cross between two Bb parents, the phenotype ratio is 3:1 purple to white.
Medium
True or false?
26.Why is genetic variation important for natural selection?
Hard
- AIt provides the raw material for adaptation
- BIt makes organisms stronger
- CIt ensures all individuals are identical
- DIt speeds up reproduction
27.Match each type of reproduction with its correct description.
Medium
- Asexual reproduction
- Sexual reproduction
- Parthenogenesis
- Offspring arise from a single parent
- Offspring arise from two parents
- An unfertilized egg grows into a new organism
28.Put the steps for creating a Punnett square in the correct order.
Medium
- Place the genes from the first parent at the top of the square.
- Place the genes from the second parent on the left side of the square.
- Pull the genes from the top into the boxes below.
- Pull the genes from the side into the boxes next to them.
29.Sex cells (gametes) contain half the number of chromosomes as body cells.
Easy
True or false?
30.Which type of reproduction would give the population a better chance of surviving the disease over many generations?
Medium
- AAsexual reproduction
- BSexual reproduction
- CBoth are equally effective
- DNeither is effective
31.Complete the sentence:
Easy
The process where a sperm and egg meet during fertilization forms a ____, the first cell of a new organism.
32.What is the term for the passing of traits from parents to offspring?
Easy
33.In humans, how many chromosomes are in a normal body cell?
Medium
34.What is the name of the process that explains the change in the peppered moth population?
Medium
35.What is the name for the male sex cell in animals?
Easy
36.In humans, how many chromosomes are in a sex cell?
Medium
37.In the Punnett square example, what percentage of offspring have purple flowers?
Easy
38.In a Punnett square for a cross between two heterozygous purple-flowered pea plants (Bb x Bb), how many offspring out of four are predicted to have white flowers?
Medium
39.Explain why asexual reproduction can be disadvantageous for a species.
Hard
40.Explain why variation is important for the survival of a species.
Medium
41.Explain why a mule, the offspring of a horse and a donkey, is not considered a new species.
Medium
42.What is the main source of genetic variation in sexually reproducing organisms?
Medium
43.In humans, how many chromosomes are in a normal body cell?
Medium
- A41
- B46
- C56
- D51
44.In humans, how many chromosomes are in a sex cell?
Medium
- A25
- B23
- C21
- D27
45.In the Punnett square example, what percentage of offspring have purple flowers?
Easy
- A75 %
- B83 %
- C67 %
- D91 %
46.In a Punnett square for a cross between two heterozygous purple-flowered pea plants (Bb x Bb), how many offspring out of four are predicted to have white flowers?
Medium
- A1
- B0
- C3
- D2
47.Farmers produced modern corn from a wild ancestor plant called teosinte by repeatedly breeding together the plants with the largest, most useful ears over many generations. Explain, in terms of offspring traits, why this breeding program depended on sexual reproduction rather than asexual reproduction.
Medium
48.A mother who carries one copy of the sickle cell allele (genotype Hh) has children with a father who has two normal haemoglobin alleles and is not a carrier (genotype HH). The diagram shows this cross. Using the diagram, explain how the chance of a child having sickle cell anaemia (genotype hh) compares with either parent having the condition.
Hard

復習ノート

## Reproduction and Genetic Variation ### Key Concepts - **Asexual reproduction** produces offspring that are **genetically identical** to the parent (clones). No variation is introduced. - **Sexual reproduction** combines DNA from two parents, creating offspring with **unique combinations of genes**, leading to genetic variation. ### Sources of Genetic Variation 1. **Mutations**: Changes in DNA sequence. They are the **ultimate source** of all genetic variation. Most mutations are neutral or harmful, but some can be beneficial. 2. **Genetic recombination (crossing over)**: During meiosis, homologous chromosomes exchange segments, creating new allele combinations. 3. **Independent assortment**: During meiosis, chromosomes line up randomly, leading to different combinations in gametes. 4. **Random fertilization**: Any sperm can fertilize any egg, increasing variation. ### Types of Genetic Variation - **Small-scale**: Base-pair substitutions, insertions, deletions (indels). - **Large-scale**: Copy number variations, chromosomal rearrangements (translocations, inversions). - **Whole chromosome/genome changes**: Polyploidy (extra sets of chromosomes), aneuploidy (extra or missing individual chromosomes). ### How Variation is Maintained - **Recessive alleles** can be hidden in heterozygotes. - **Balanced polymorphisms**: Heterozygotes may be favored (e.g., sickle cell trait and malaria resistance). ### Key Terms - **Allele**: Different versions of a gene. - **Heterozygous**: Having two different alleles for a gene. - **Polymorphism**: Presence of multiple alleles at a locus in a population. ### Remember - Variation is essential for natural selection and evolution. - Without variation, a population cannot adapt to changing environments.

Asexual reproduction: Reproduction that produces genetically identical offspring from a single parent.
Sexual reproduction: Reproduction involving the fusion of gametes from two parents, producing genetically diverse offspring.
Mutation: A change in the DNA sequence that can create new alleles and is the ultimate source of genetic variation.
Genetic recombination: The exchange of genetic material between homologous chromosomes during meiosis, leading to new combinations of alleles.
Allele: One of two or more versions of a gene.
Heterozygous: Having two different alleles for a particular gene.
Polymorphism: The occurrence of two or more distinct alleles at a gene locus in a population.
Polyploidy: A condition in which an organism has more than two complete sets of chromosomes.

フラッシュカード

What is the main difference between offspring from asexual reproduction and sexual reproduction?

Asexual reproduction produces genetically identical offspring (clones), while sexual reproduction produces offspring with genetic variation.

Define genetic variation.

Genetic variation is the difference in DNA sequences among individuals or between populations of the same species.

What is the ultimate source of all genetic variation?

Random mutations are the ultimate source of genetic variation.

Name three processes during sexual reproduction that increase genetic variation.

Crossing over (genetic recombination), random segregation of chromosomes during meiosis, and random fertilization.

What is crossing over and when does it occur?

Crossing over is the exchange of genetic material between homologous chromosomes during meiosis, producing new combinations of alleles.

How does random fertilization contribute to genetic variation?

Random fertilization means any sperm can fuse with any egg, creating many possible zygote combinations.

What is a mutation?

A mutation is a change in the DNA sequence, which can be a base-pair substitution, insertion, or deletion.

Are most mutations harmful, neutral, or beneficial?

Most mutations are neutral or harmful; only rarely are they beneficial.

What is polyploidy?

Polyploidy is a condition where an organism has three or more complete sets of chromosomes (3n or more).

What is the difference between a gene and an allele?

A gene is a segment of DNA that codes for a trait; an allele is a specific version of that gene.

What does it mean for a gene to be polymorphic?

A polymorphic gene has more than one allele present in the population.

How can genetic variation be observed without looking at DNA?

By observing phenotypic variation in traits, such as continuous traits (e.g., height) or discrete traits (e.g., flower color).

What is geographic variation?

Geographic variation is genetic differences between populations that are separated by geography.

Name three factors that can cause geographic variation.

Natural selection, genetic drift, and gene flow.

What is a balanced polymorphism?

A balanced polymorphism occurs when natural selection maintains two or more alleles in a population, often because heterozygotes are favored.

How can harmful recessive alleles persist in a population?

They can be hidden in heterozygous individuals, where the dominant allele masks the recessive one.

What is the difference between a somatic mutation and a germline mutation?

A somatic mutation occurs in body cells and is not passed to offspring; a germline mutation occurs in sex cells and can be inherited.

What is an indel?

An indel is a small-scale mutation involving insertion or deletion of nucleotides in DNA.

What is a chromosomal rearrangement?

A chromosomal rearrangement is a large-scale structural change in a chromosome, such as translocation or inversion.

How do RNA viruses generate genetic variation?

RNA viruses have high mutation rates due to lack of proofreading, and they can also undergo genetic recombination.

What is the role of genetic recombination in RNA viruses?

Recombination helps RNA viruses repair genome damage and generate new variants, sometimes causing outbreaks.

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