General Biology II: Chapter 15

The Chromosomal Basis of Inheritance

How many genes does each chromosome have?

100s or 1000s of genes

Thomas Hunt Morgan demonstrated what?

the physical basis in Mendelian’s inheritance (his findings supported chromosome theory of inheritance)

Wild Type

normal phenotypes

Mutant Phenotypes

alternative traits to wild type

Sex Determining Chromosomes

large X and small Y

Different Chromosomal Systems of Sex

X chromosomes: autosomes, temperature, XX vs. X, fertilized vs. unfertilized

Sex-Linked Gene

a gene located on either sex chromosome

Y-Linked Genes

genes on Y chromosomes

How many alleles does an X chromosome have?

over 1000 alleles

How many alleles does a Y chromosome have?

9 alleles (sperm production, 1 gene SRY, producing male anatomical traits)

Who is affected more by X-Linked Recessive Disorders?

males affected more than females, traits skip generations

How do males get X-Linked Recessive Disorders?

Born with unaffected mothers, ½ of carrier mothers’ sons are affected, never passed form father to son, all daughters are carriers

X-Linked Gene

gene on X chromosome, follow specific patterns of inheritance

Males are more affected by X-Linked traits, and it’s going to have what?

hemizygous for X chromosome

Females need how many copies of alleles?

2 copies, (homozygous)

Males need how many copies of alleles?

1 copy (hemizygous)

What are some X-Linked Recessive Disorders?

color blindness, duchenne muscular dystrophy, hemophelia

Duchenne Muscular Dystrophy

absence of key muscle protein called dystrophin

Hemophilia

absence of blood clotting protein “The Royal Disease”

What will females be if they’re heterozygous for a particular gene?

mosaic

What is the explanation for patches of color in cats?

random X inactivation

Genes located near each other on the same chromosome tend to?

be inherited together

Linkage Group

term used to identify groups of alleles in a chromosome that tend to be inherited together

What is the relationship between recombinant frequency and physical distance between the two genes?

the closer the genes are, the lower the chance of recombination

Parental Types

offspring with a phenotype matching one parental phenotype

Recombinant Types/Recombinants

Offspring with non-parental phenotypes (new combination of traits)

When does Crossing over occur?

Prophase I of Meiosis I

Recombination + Random Fertilization means what?

abundance of genetic variation (natural selection)

Alterations of chromosome number or structure cause what?

genetic disorders

Nondisjunction

chromosomes are sticky (do not separate normally during meiosis)

Aneuploidy

results from fertilization of gametes in which nondisjunction occurred (abnormal number of a particular chromosome)

Monosomic Zygote

has 1 copy of a particular chromosome

Trisomic Zygote

has 3 copies of a particular chromosome

Down Syndrome

aneuploid condition which results from 3 copies of chromosome 21

A couple has a child with down syndrome, which of the following is the cause of it?

one of its chromosomes went through disjunction during meiosis I

Turner’s Syndrome (Monosomy X)

produces X0 females (missing X chromosome)

Trisomy X Syndrome

XXX females have an extra X chromosome

Klinefelter’s Syndrome

Male has an extra X chromosome and is sterile (XXY)

Polyploidy

condition in which an organism has more than 2 complete sets of chromosomes (3n, 4n)

Chromosomal Deletion

syndrome cri du chat (cry of the cat) results from a specific deletion of chromosome 5