Mendelian Genetics and Meiosis

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Questions and Answers

What forms when a sperm and an egg fuse during reproduction?

A diploid organism

A zygote with a full set of chromosomes (correct)

A gamete with half the number of chromosomes

A Punnett grid

What is the term for the offspring of a cross between two plants?

Gamete

F1 generation (correct)

P generation

Punnett grid

What is the purpose of using a brush during plant crosses?

To analyze the cross

To create a Punnett grid

To prevent unwanted pollination (correct)

To transfer pollen to the stigma

What is the term for the combination of alleles inherited by an organism?

Genotype Signup and view all the answers

What is the term for an individual with two identical alleles?

Homozygous Signup and view all the answers

What is the term for an individual with different alleles?

Heterozygous Signup and view all the answers

What is the purpose of a Punnett grid?

To analyze the cross between two plants Signup and view all the answers

What is the term for different versions of a gene?

Allele Signup and view all the answers

What is the purpose of understanding the movements of chromosomes in meiosis?

To understand the segregation and independent assortment of unlinked genes Signup and view all the answers

What is the expected phenotypic ratio in a dihybrid cross involving unlinked autosomal genes?

9:3:3:1 Signup and view all the answers

What is the significance of using vertical lines to represent homologous chromosomes in a cross?

To show the alleles of linked genes Signup and view all the answers

Why do alleles of linked genes fail to assort independently?

Because they are located on the same chromosome Signup and view all the answers

What is the purpose of using a chi-squared test in dihybrid crosses?

To determine the statistical significance of the results Signup and view all the answers

What is the concept of statistical significance related to in a chi-squared test?

The p = 0.05 level Signup and view all the answers

What is the result of non-disjunction during meiosis?

Cells with an extra or missing chromosome Signup and view all the answers

What is the exception to the rule of non-disjunction being lethal?

Down syndrome Signup and view all the answers

What occurs during crossing over in meiosis?

Non-sister chromatids in a bivalent swap sections of DNA Signup and view all the answers

What is the result of crossing over in meiosis?

New combinations of alleles are created on the chromosomes Signup and view all the answers

What determines which alleles end up in each gamete during meiosis I?

Random orientation of bivalents Signup and view all the answers

What is the number of possible gamete combinations generated by the random orientation of bivalents in humans?

Over 8 million Signup and view all the answers

What is the role of spindle fibers in meiosis I?

They attach to each chromosome and determine which pole it will attach to Signup and view all the answers

What is the outcome of the random orientation of multiple bivalents in meiosis I?

A vast number of possible gamete combinations Signup and view all the answers

Study Notes

Meiosis and Genetic Diversity

Meiosis generates genetic diversity through random orientation of bivalents and crossing over.
Crossing over occurs when non-sister chromatids in a bivalent swap sections of DNA, resulting in an exchange of genes.
This exchange creates new combinations of alleles on the chromosomes, increasing genetic diversity in offspring.

Random Orientation of Bivalents

In meiosis I, bivalents line up in the center of the cell, and spindle fibers attach to each chromosome, but which pole they attach to is random (50% chance for either).
The random orientation determines which alleles end up in each gamete (sperm or egg).
The random orientation of multiple bivalents creates a vast number of possible combinations (2^n, where n is the number of bivalents).

Dihybrid Crosses

Students should understand how Punnett grids predict genotypic and phenotypic ratios in dihybrid crosses involving pairs of unlinked autosomal genes.
The 9:3:3:1 and 1:1:1:1 ratios are derived from Punnett grids.

Autosomal Gene Linkage

In crosses involving linkage, alleles of linked genes can fail to assort independently.
The symbols used to denote alleles should be shown alongside vertical lines representing homologous chromosomes.

Recombinants

Students should understand how to determine the outcomes of crosses between an individual heterozygous for both genes and an individual homozygous recessive for both genes.
Identify recombinants in gametes, genotypes of offspring, and phenotypes of offspring.

Chi-Squared Test

Students should understand the concept of statistical significance, the p = 0.05 level, null/alternative hypothesis, and the idea of observed versus expected results.

Non-Disjunction and Chromosomal Abnormalities

Errors can occur during meiosis where chromosomes don't separate properly, leading to cells with an extra or missing chromosome, usually lethal.
Down syndrome is a rare exception where having an extra chromosome (number 21) isn't fatal, but causes developmental problems.
Non-disjunction can also cause sex chromosome abnormalities like Klinefelter's syndrome (XXY) and Turner's syndrome (X).

Genotype and Alleles

Genotype is the combination of alleles inherited by an organism.
Individuals with two identical alleles (BB or bb) are homozygous, while those with different alleles (Bd) are heterozygous.
Genes can have different versions, called alleles, which can arise from mutations.

Genetic Crosses in Flowering Plants

Genetic crosses are widely used to breed new varieties of crop or ornamental plants.
Pollination is needed to carry out a cross, and plants such as peas produce both male and female gametes on the same plant, allowing self-pollination and self-fertilization.
Scientists study inheritance patterns by crossing flower varieties like peas, using Punnett squares to analyze the crosses.

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Description

Understand the principles of Mendelian genetics, including segregation, independent assortment, and Punnett grids for predicting genotypic and phenotypic ratios in dihybrid crosses.