CHAPTER 11:CHROMOSOMES AND HUMAN INHERITANCE

HUMAN CHROMOSOMES

Most animals have a _________number of chromosomes: _____

Humans have ____ pairs of chromosomes All (except one) of those pairs are called

_______________ Same length, shape, and centromere

location Humans have ___

______ _______________ are the last pair

SEX CHROMOSOMES

Sex chromosomes determine ________

Males : ___

Females: ____

X and Y chromosomes differ in length, shape, and the genes they carry

___ __________

Each egg contains 22 autosomes + an X chromosome

Sperm will contain 22 autosomes + either an X chromosome OR a Y chromosome

Egg and sperm combine either XX (female) or XY (male)

Reference figure 11.2, pg. 170

SEX DETERMINATION: Y CHROMOSOME

Fewer than two dozen genes identified

The Y chromosomes carries the ____ ______

Master gene for male sex determination

Expression of SRY gene triggers formation of ________ , which are the primary male sex organs (or gonads)

These secrete ________________, which is responsible for the male secondary sex traits

SEX DETERMINATION

Absence of the male-determining SRY gene in females results in the formation of ovaries

Mutations in the SRY gene causes individuals who are XY to develop as females

The X chromosome codes for sexual traits but ALSO carries many genes for nonsexual traits

X chromosome carries over ______ genes

Males only have one copy of these genesReference figure 11.2

KARYOTYPING

A _____________ is a diagnostic tool that is a preparation of an individual’s metaphase chromosomes

Mitosis is arrested in _________ Chromosomes are photographed, and

then cut out and arranged by pairs according to size, shape, and length

Array can be compared to a normal standard and analyzed for extra or missing chromosomes

KARYOTYPING

Figure 11.3, pg. 171

HUMAN GENETIC ANALYSIS

Humans are difficult to study genetically due to long life spans (compared to a fruit fly or a garden pea) and small families

Data on human inheritance is displayed in _________________

A pedigree is a chart that shows genetic connections among individuals

Analysis of family pedigrees provides data on inheritance patterns through several generations

PEDIGREES

Knowledge of ______________ and ________________________________ is used in analysis of pedigrees to yield clues to a trait’s genetic basis

Conclusions most accurate when drawn from large number of pedigrees

Can be used to predict the risk of disease in future offspring in a family (genetic counseling)

PEDIGREES

Uses standardized symbols: Squares = ________ , Circles = ______ Shaded squares/circles = those who carry

trait of interest Horizontal line between male/female =

__________________ Number generations from oldest (top) to

youngest (bottom) with Roman numerals Number individuals within a generation from

oldest (left) to youngest (right) with Arabic numerals

EXAMPLE PEDIGREE

A PEDIGREE FOR POLYDACTYLY

Polydactyly: An unusual number of fingers of toes

Figure 11.17, pg. 180

GENETIC DEVIATIONS

Genetic ________________ is a term applied to a genetic condition that is a deviation for the usual (or average) and is not life-threatening Rare or less common version of a trait

Genetic ______________ is used to describe conditions that cause medical problems

______________ is a recognized set of symptoms that characterize an abnormality or disorder

A disease is an illness caused by infection or environmental factors A genetic _____________ is a term used only when

factors alter previously workable genes in a way that disrupts body functions

AUTOSOMAL INHERITANCE PATTERNS

Some alleles on autosomes are inherited in simple Mendelian patterns

Certain mutated forms of alleles give rise to genetic abnormalities or genetic disorders

______________________

Figure 11.4a, pg. 172

AUTOSOMAL DOMINANT INHERITANCE

The dominant allele is nearly always expressed, even in heterozygotes

If one parent is heterozygous and the other homozygous recessive, there is a 50% chance that their child will be heterozygous

If the gene (and its resulting disorder) reduces the chance of surviving or reproducing, its frequency should decrease

However, it may not due to:

EXAMPLES: AUTOSOMAL

DOMINANT Acondroplasia (dwarfism)

A benign abnormality that does not affect persons’ ability to reproduce

Adults have abnormally short arms and legs

Huntington disease A serious degeneration of the nervous

system with an onset from age 40 onwards At this point, the gene has typically been

passed from parent to offspring unknowingly

____________________

AUTOSOMAL RECESSIVE

INHERITANCE Either parent can carry the recessive allele on

an autosome

Heterozygotes are symptom-free; homozygotes are affected

Two heterozygous parents have a 50% chance of producing heterozygous children and a 25 percent chance of producing a homozygous-recessive child

When both parents are homozygous, all children can be affected

EXAMPLE: AUTOSOMAL

RECESSIVE Galactosemia: the inability to metabolize

lactose

A single gene mutation prevents the manufacture of an enzyme needed in the conversion pathway

Lactose galactose glucose-6-phosphate, which can be converted to glycogen or enter glycolysis

NUEROBIOLOGICAL DISORDERS

Nuerobiological disoders (NBDs) include:

Changes in genes contribute to the abnormal biochemistry in NBDs

Most NBDs involve multiple genes and environment factors – not just a single allele

Some mutated alleles are linked to these disorders and can predispose a person

HUTCHINSON-GILFORD PROGERIA SYNDROME

Premature aging is caused by a mutated allele

In one of 8 million newborn humans, a mutated gene will cause accelerated aging

Observable symptoms arise by age two

Their skin thins, skeletal muscles weaken, bone growth ceases, hair loss occurs, and they “look old”

Most progeriacs expect to die in their teens

______ INHERITANCE PATTERNS

Certain dominant and recessive alleles on the X chromosome are inherited in Mendelian patterns

Approximately _________ of all genes are located on the X chromosome

Mutated alleles on the X chromosome contribute to more than 300 known genetic disorders

Males can’t transmit X-linked alleles to sons:

X-LINKED INHERITANCE

In X-linked recessive inheritance, the mutated gene occurs only on the X chromosome

Males are more often affected because a single recessive allele on the X chromosome cannot be masked by a dominant gene on another chromosome

Heterozygous females are phenotypically normal

X-LINKED INHERITANCE

X-LINKED INHERITANCE

A normal male mated with a female heterozygote (or carrier):

Homozygous recessive female and a normal male:

HEMOPHILIA A

Hemophilia is a serious X-linked recessive condition that prevents blood from clotting properly

The blood cannot clot because the genes do not code for the necessary clotting agent or agents

Today, hemophilia affects about 1 in 7,500 people

This number may be increasing because hemophilia is now treatable

RED-GREEN COLOR BLINDNESS

Color blindness is the inability to distinguish colors

Mutated genes change the light-absorbing capacity of sensory receptors in the eyes

Normal people can distinguish among 150 colors

People with red-green color blindness can only see 25 colors (or fewer)

Males are 12 times more likely than women to be affected by color blindness

DUCHENNE MUSCULAR DYSTROPHY

Duchenne Muscular Dystrophy (DMD) affects about 1 in 3,500 boys

It’s characterized by a rapid degeneration of muscles

A recessive allele encodes for dystrophin, a structural protein in muscle fibers

Abnormal or absent dystrophin causes the muscle degeneration