Chapter 6 Meiosis and Genetic Variation

Are chromosomes in a duplicated or an unduplicated state when crossing over occurs?

Chromosomes are in an unduplicated state when crossing over

Mendel's Choices Observations involving "either-or traits that occur in alternate forms.

Comparing between a purebred model and an altered one.

means one of each trait-a pari of alleles that are different

Heterozygous

Whose early work is the basis for much of our current understanding of genetics?

Mendel's

During which phase do homologous chromosomes separate?

Metaphase I

Why did Mendel use pea plants?

Pea plants are unique in that they can come in several forms. Therefore it is easy to make observations and compare one another.

The appearance of the traits. Determines how the genes will show physically within the organism

Phenotype

Two chromosomes that are very similar and carry the same genes are called

homologous chromosomes

Sex Chromosomoes

include Egg Cells include Ovaries/Testies

The term for a cross that involves just one trait, such as pod shape, is called a

monohybrid cross

Mendel was able to identify predictable patterns of heredity. He succeeded mainly because he chose to study traits that

had only two forms

When Mendel crossed plants that were purebred purple-flowered with plants that were purebred white-flowered, the resulting offspring all had purple flowers. When allowed to self-pollinate, this F1 generation gave rise to white-flowered plants as well as purple. As a result, Mendel determined that individual traits are

inherited as discrete units

Probability

predicts the exact number of occurrences, not the theoretical number of occurrences.

An experimental way to find the answers to questions such as how many times a coin will show heads vs. tails

probability

What is the probability that the offspring of a cross between a homozygous recessive parent and the heterozygous parent will be homozygous recessive?

1/4

What is the phenotypic ratio of a monohybrid cross between two heterozygous parents?

1:2:2:1

Ratios Heterozygous

1:3:1

7. If genes A and B are located very close together on the same chromosome, are they likely to follow Mendel's law of independent assortment? Explain.

Absolutely, because they are close enough in such a way to the point that they can easily attach to one another to form a pair.

An alternate form of a gene that occurs at a particular locusWhat is the relationship between a gene and a protein?

Allele

How are alleles represented on paper?

Allelles can be represented as alternate copies of a gene.

Mendel's Choices Breeding control

Altering the plants so that they are slightly different from their original species (e.g, removing stamens_

What is an alternative form of a gene?

An allele is an alternate form to a gene.

Crosses that happen between two genotypes

Dihybrid Cross

Which of the following observations did Mendel make as a result of his experiments with dihybrid crosses?

Dominant traits are inherited together

What two conclusions make up Mendel's law of segregation?

Each organism inherits tewo copies of each gene, one from the mother and one from the father. Organisms only give one gene to their gamete cells

Where are gametes located?

Gametes are located in your sex organs.

What is independent in the law of independent assortment?

Genes are independent according to the law of Independent Assortment

Segregation means "separation." What is "segregated" in Mendel's law of segregation?

Genes are segregated in Mendel's law of segregation.

What is the relationship between a gene and a protein?

Genes are used to code for proteins.

Mendel concluded that traits are inherited as "discrete units." What do we call these discrete units today?

Genes.

What is genetics?

Genetics is the study of traits, how they are formed, and what they do.

A set of genes that are inherited by offspring

Genome

What factors besides alleles affect phenotype?

Genotype can affect phenotype, as well as trait type. (Dominant or recessive)

Punnett Square Grid Boxes

Genotypes

46 Chromosomes in Human Body Cells

Half come from Mother Half come from Father

What are homologous chromosomes?

Homologous chromosomes are two-sided chromosomes. There are two pairs, one from the mother, and one from the father.

Genesis comes from a Greek word that means "to be born." How does this relate to the meaning of gametogenesis?

If genesis means birth, than gametogenesis must involve the birth of something. That something is a gamete.

The word soma means "body." How does this relate to the meanings of autosome and somatic cell?

If soma means body, then both somatic cells and autosomes can be found in the body.

46 Chromosomes in Human Body Cells

Include Sex Chromosomes Include Sperm Cells

Meiosis

Involves gametes. Makes genetically unique cells Two separate cycles process and break down chromosomes. Involved in sexual reproduction

How is the production of unique genetic combinations an advantage to organisms and species?

It creates sexual diversity, even amongst organisms and species.

If genes A and B are located on separate, non homologous chromosomes, will they follow Mendel's law of independent assortment? Explain.

No, because homologous chromosomes are set up randomly and can change. Non homologous chromosomes cannot.

If an organism has a recessive trait, can you determine its genotype for that trait?

No. Genotypes can only be determined using dominate traits.

If genes A and B are located at opposite ends on the same chromosome, are they likely to follow Mendel's law of independent assortment? Explain.

Not likely, because of their distance from each other.

Which of the following conclusions was a result of Mendel's observations

Organisms inherit two copies of each gene, on from each parent

Genotype Homozygous dominant

Phenotype Alleles Dominant TT

Genotype Heterozygous Dominant

Phenotype Alleles Dominant Tt

Genotype Heterozygous Recessive

Phenotype Alleles recessive tT

Punnett Square Axes

Phenotypes

Where are polar bodies made, in the male or in the female?

Polar bodies are made in the male.

What are two ways that sexual reproduction helps create and maintain genetic diversity?

Sexual reproduction is important, because to uses chromosomes that randomly select pairs of genes to create genetic diversity.

Used as letters such as F and f.

Symbols

A cross between an organism with an unknown genotype and a recessive phenotype. Crosses that do not affect genotype

Testcross

Which chromosome carries the fewest number of genes?

The 23rd chromosome carries the fewest number of genes.

What is the opposite of homozygous? of dominant?

The opposite of homozygous is heterozygous. As such, the opposite of dominant is recessive.

What does "purebred" mean?

The organism is completely original, thus the organism is not "mixed" between two species or breedings.

How many autosomes are present in each human gamete? How many sex chromosomes?

There are 21 autosomes in each sex cell. The other two are sex chromosomes.

3. How many chromosomes are in a typical human body cell?

There are 23 chromosomes per each human cell

What is the haploid chromosome number in humans?

There are two haploid chromosomes per human cells.

What is a dihybrid cross?

These are crosses that involve two traits.

What type of alleles are present in an organism with a QQ genotype?

They are both dominant traits.

Why does each parent contribute only one allele to the offspring?

They do this because two of them is too much for an organism to handle.

What happens to the nuclei of the egg and sperm during fertilization?

They fuse together to form an embryo.

Ratios Homozygous

2:2:0

Write a definition of homologous chromosomes using the terms "gene" and "allele."

A homologous chromosome is comprised of two alleles, each coding for a particular gene. One comes from the mother, another from the father.

What is a polar body?

A polar body is a somewhat prototupe of what an embryo will look like once it is born.

Suppose an organism had the genotype AABb. What two types of gametes could result from this allele combination?

ABab, AbaB

represented by capital letters

Dominant

What is the sex of a person with two X chromosomes?

Female

What are the two major groups of cell types in the human body?

Gametes and Somatic Cells.

means two of the same trait- a pair of alleles that are the same

Homozygous

This law states that genes may be paired in such a way that they are decided using probability

Law of independent assortment

Mitosis

Makes diploid cells Asexual Reproduction Happens throughout lifetime A cycle of phases breaks down chromosomes and prepares the cell for division.

How did Mendel's views on inheritance differ from the views of many scientists of his time?

Many scientists believed that inheritance was governed by proteins rather than discrete traits.

During which phase do sister chromatids separate?

Metaphase II

represented by lower case letter

Recessent

Which does sexual reproduction create, new alleles or new combinations of alleles?

Sexual reproduction creates new combinations of allelles.

What does an egg contribute to an embryo?

The egg cell is the "mother" cell for the embryo. Itt contains the embryo. To form the embryo, it first must fuse with the sperm cell.

Write an analogy to show the difference between genotype and phenotype.

The engine and gasoline tanks make up the interior functioning in a car. However, the physical characteristics (like a phenotype) determines the cars type according to it's exterior

You know a ratio is a comparison that tells how two or more things relate. What is a genotypic ratio? a phenotypic ratio

The genotypic ratio is the ratio of gene makeup to genes themselves. Similarly, a phenotypic ration illustrates a connection between traits and genes

What does a sperm cell contribute to an embryo?

The sperm cell is the "father" cell for the embryo. It fuses with the egg to form the embryo.

Mendel's Choices Use of purebred plans

Using an original species rather than a modified version.

What is the phenotypic ratio that results from a dihybrid cross between two organisms that are heterozygous for both traits

YyRr

After a chromosome is replicated, each half is called a

chromatid

Sperm Cells

consist of 22 homologous pairs

The exchange of chromosome segments between homologous chromosomes is called

crossing over

An example of a biological trait is

eye color

What type of cells are haploid?

gametes are known as haploid cells.

The tendency for two genes that are located close together on a chromosome to be inherited together is called

genetic linkage

What do the letters inside the grid of a Punnett square represent?

genotypes of offspring

Mendel began his experiments with purebred pea plants. This approach enabled him to determine that variations among offspring were the result of

self-pollination