Exam 1 Book

Mendel’s Law of Independent Assortment

Genes for different traits assort independently during gamete formation if they are unlinked or far apart on chromosomes

When genes do NOT assort independently

When genes are on the same chromosome and closely linked

Product rule

The probability of two independent events occurring together equals the product of their probabilities

Product rule example (dice)

P(rolling two 4’s) = 1/6 × 1/6 = 1/36

Sum rule

The probability of either of two mutually exclusive events is the sum of their probabilities

Sum rule example (dice)

P(rolling a 4 or 5) = 1/6 + 1/6 = 1/3

Finding probability in multi-trait crosses

Multiply each trait’s probability together

Polygenes

Genes that each have a small additive effect on a trait

Quantitative trait locus (QTL)

A gene contributing to variation in a quantitative trait

Examples of polygenic traits

Height and weight

Location of polygenes

Often on different chromosomes and show independent assortment

Cytoplasmic inheritance

Inheritance of genes in organelles like mitochondria or chloroplasts

Mitochondrial DNA (mtDNA)

DNA in mitochondria encoding some organelle functions

Chloroplast DNA (cpDNA)

DNA in chloroplasts involved in photosynthesis

Uniparental inheritance

Offspring inherit organelle genes from only one parent

Maternal inheritance

Inheritance of organelle genes from the mother

Why cytoplasmic inheritance is usually maternal

The egg contributes most of the cytoplasm

Mutant female × wild-type male (cytoplasmic inheritance)

All offspring mutant

Wild-type female × mutant male (cytoplasmic inheritance)

All offspring wild type

Assumption for normal female in rare X-linked recessive pedigree

Homozygous unless evidence suggests otherwise

Examples of X-linked recessive disorders

Red-green color blindness and hemophilia

X-linked dominant affected male transmission

All daughters affected and no sons

X-linked dominant heterozygous female transmission

Half of sons and half of daughters affected

Y-linked inheritance

Inherited only by males

Y-linked transmission

Father to son

SRY gene

Gene on Y chromosome that determines maleness

Male sterility heritability

Not heritable

What is a character or trait?

An attribute of individual members of a species that can vary

What is the goal of the genetic approach?

To identify genes that influence a biological trait

What is the basic approach of genetics?

Compare variants to wild type to deduce gene function

What is wild type?

The most common form of a trait in an organism

What is a mutant?

A heritable variant that differs from wild type

What is phenotype?

The observable form taken by a character

What is a mutation?

A heritable change in the DNA of a gene

What is genetic dissection?

Using recombination and mutation to analyze components of biological function

What is forward genetics?

Studying random mutants to identify genes involved in a process

What is single-gene inheritance?

Inheritance controlled by one gene

What did Mendel use to study inheritance?

Pea plants

What is the parental generation?

The original strains used in a cross

What is the F1 generation?

Offspring from a cross of two parental individuals

What is the F2 generation?

Offspring from a cross between F1 individuals

What ratio did Mendel observe in the F2 generation?

3:1

What is Mendel’s Law of Equal Segregation?

Alleles separate equally into gametes

What is a zygote?

A fertilized egg

What is a homozygote?

An individual with two identical alleles

What is a heterozygote?

An individual with two different alleles

What is a monohybrid cross?

A cross tracking one gene

What is a homozygous dominant genotype?

YY

What is a homozygous recessive genotype?

yy

What are sex chromosomes?

Chromosomes involved in sex determination

What sex chromosome combination do human females have?

XX

What sex chromosome combination do human males have?

XY

Which sex is homogametic in humans?

Females

Which sex is heterogametic in humans?

Males

What does hemizygous mean?

Having only one copy of a gene in a diploid organism

What is sex linkage?

Genes located on sex chromosomes that show distinct inheritance patterns

What is X-linkage?

Inheritance patterns of genes on the X chromosome

What is Y-linkage?

Inheritance patterns of genes on the Y chromosome

What are pseudoautosomal regions?

Small homologous regions at the ends of X and Y chromosomes

Why are pseudoautosomal regions important?

They allow pairing and crossing over during meiosis

What is sex-limited inheritance?

Genes on sex chromosomes not necessarily related to sexual function

What is an example of sex-linked inheritance?

Red eye color in Drosophila

What is pedigree analysis?

Using family history to deduce inheritance patterns

Who is the proband?

The individual who brings a genetic condition to attention

Why is pedigree analysis used?

To track inheritance across generations

What defines an autosomal recessive disorder?

Affected phenotype inherited only when two recessive alleles are present

How do autosomal recessive disorders usually appear in families?

In offspring of unaffected parents

Who can be affected by autosomal recessive disorders?

Both males and females equally

What genotype do most carriers have?

Heterozygous

What defines an autosomal dominant disorder?

A single dominant allele causes the disorder

How do autosomal dominant traits appear across generations?

They usually appear in every generation

Are males and females equally affected in autosomal inheritance?

Yes

What is a polymorphism?

Coexistence of two or more common phenotypes in a population

How are polymorphisms usually inherited?

As alleles of a single autosomal gene

What is dimorphism?

A polymorphism with only two forms

What is somatic cell division?

Division of body cells

What type of division do somatic cells undergo?

Mitosis

What is produced by mitosis?

Two identical daughter cells

What is sexual cell division?

Division producing gametes

What type of division produces gametes?

Meiosis

What cells divide during meiosis?

Specialized cells called meiocytes