Download Oct genetics Part 2 final 2025

A. Disorders Caused by Recessive Alleles
Some disorders caused by recessive alleles on
autosomes
(dominant)
A person who is heterozygous for disease is called
a carrier- does not show disease symptoms
•
Must have two copies of recessive allele to have disorder
•
Disorders often appear in offspring of parents who are
heterozygous
Cystic fibrosis (CF).
• Is a genetic disease that causes the lungs to produce a
thick, sticky mucus.
• This mucus blocks the airways and allows
microorganisms to thrive in the lungs.
• People with CF have frequent, sometimes fatal, lung
infections.
• Treatments focus on preventing the mucus from
building up.
•
The most common lethal genetic disease in the U.S.
1 out of 25 Caucasians is a carrier.
B. Disorders Caused by Dominant Alleles
• Less common than recessive disorders
Ex. Huntington’s Disease
• A degenerate disease of the nervous system resulting in
certain and early death. Onset is usually in middle age.
• 75% chance if both parents heterozygous
• Since disease strikes later in life, person can have children
before disease appears. Allele is passed on even though
disease is fatal
Sex-Linked Genes
• Males and Females can differ in sex-linked traits
• Expression of genes on sex chromosomes
differs from autosomal genes
• Mendel only studied autosomal traits
• Genes located on sex-chromosomes called
sex-linked genes
• Expression of Sex-Linked Genes
•
Males only have one copy of each chromosome (XY)
•
Thus Express all alleles on each chromosome
Color Blindness
•
•
•
•
Sex linked recessive disorder
Occurs when you are unable to see colors in a normal way.
Often happens when someone cannot distinguish between
certain colors.
This usually happens between greens and reds, and
occasionally blues
X Chromosome Inactivation
•In each cell of female, one of two X-chromosome is
randomly “turned off”.
•This will creates patchwork of two types of cells
Complex Patterns of Inheritance
A. Incomplete Dominance
• Neither allele completely dominant
• Heterozygous phenotype somewhere
between homozygous phenotypes (“blending”)
• Give intermediate trait
Phenotype Genotype
green
B1B1
Phenotype Genotype
Phenotype Genotype
Steel blue
Royal blue
B2B2
B1B2
B. Codominance
•
Both traits are expressed completely
• mixture of both traits
ef0030_white-cow_small
X
red
=
white
roan
❖ Human blood type is example of
1) Codominance, between A & B
2) Multiple-Allelic Trait, 3 different alleles A, B, O
3) Complete Dominance between A & O, B & O
C. Polygenic Traits
two or more genes determine trait
a. Skin color result of four genes that interact to
produce range of colors
b. Human eye color
c. Humans Height
Albinism
is a autosomal recessive trait. Because the allele is recessive,
individuals who are heterozygous for the trait express their
normal skin color, so the presence of the allele is “hidden” by the
dominance of the normal allele. Albinos are unable to
synthesize melanin, the pigment molecule responsible for most
human skin coloring
The environment interacts with genotype
•Phenotype is more than sum of gene expression
• Sex of sea turtles depends on genes and environment.
• Temperature when eggs develop determine sex
• If a turtle's eggs incubate below 81.86 Fahrenheit , the turtle
hatchlings will be male
• If the eggs incubate above 87.8° Fahrenheit , however, the
hatchlings will be female
•
Human traits also affected by environment
(nutrition and health care)
Family Pedigree
A pedigree is a chart for tracing genes in a family
1. Phenotypes are used to infer genotypes on
a pedigree
2. Autosomal genes show different patterns on a
pedigree than sex-linked genes.
HUMAN GENOME
• contains 20-000 to 30,000 genes. Much lower than earlier
estimates of 80,000 to 140,000
1. Contains 3164.7 million chemical
nucleotide bases (A, C, T and G)
2. 99.9% of all nucleotide bases are
exactly the same in all people
3. Less than 2% of genome actually
codes for proteins
Karyotypes
• picture of all chromosomes in a cell
• To determine 1) Diploid Number
2) Sex
3) Chromosomal abnormalaties
Down syndrome
• is a genetic disorder caused when abnormal cell
division results in an extra copy of chromosome 21
•Nondisjunction during meiosis cause this syndrom
Sex Chromosome disorders
• In Females, Nondisjunction can lead to
Turner’s Syndrome (XO) sex organs fail
to develop at puberty
No Y chromosome
In Males, Nondisjunction causes Klinefelter’s
syndrome (XXY) extra X interferes with meiosis
and usually prevents individuals from reproducing
Cri-du-chat (cat's cry) syndrome
•
also known as 5p- (5p minus) syndrome,
•
is a chromosomal condition that results when a piece of
chromosome 5 is missing .
•
Infants with this condition often have a high-pitched cry that
sounds like that of a cat.