This document discusses several patterns of inheritance including: 1. Dominant and recessive genes and how they determine traits like coat color in mice. 2. Lethal alleles that cause death in homozygous dominant genotypes. 3. Incomplete dominance and codominance where both alleles are partially or fully expressed. 4. Sex linkage and how traits on the X chromosome are inherited differently between males and females. It also discusses environmental influences on gene expression and abnormal chromosome numbers leading to conditions like Down syndrome.

1. Patterns of
Inheritance
How genes interact and are
influenced to produce
different traits.

2. Review - Simple Mendelian Genetics
 Dominant gene
covers other allele
• Ss or SS genotype
yields smooth coat
 Recessive gene is
only expressed
when dominant
allele is not
inherited
• ss genotype
yields long coat

3. Lethal Allele Combinations
 The yellow fur color allele is
dominant (Y)
• however, it's only expressed in
heterozygous Yy mice
 Homozygous dominant (YY)
mice never appear (they die
before birth)
 Homozygous recessive (yy)
mice are white
 Even though the fur color Y is
dominant, the lethal allele is
considered recessive because
it only appears in the
homozygous YY genotype.

4. Incomplete Dominance
 Heterozygotes (CRCW) express
an intermediate phenotype
(pink)
 Instead of overpowering one
another, both traits are
partially expressed
 Flower color traits separate
again during meiosis and can
be seen in the F2 generation

5. Codominance
 The inheritance of ABO • Two alleles are dominant
blood groups demonstrates • Type A and Type B
codominant inheritance • (Type O is recessive)
• Both phenotypes are
expressed in the
heterozygote (Type AB)

6. Codominance
 B = black
X  W = white
 What would the
genotype of each
of these chickens
have to be?

7. Multiple Alleles
 The ABO blood type is an example of a trait that has more
than just two different alleles (A, B, and O)
 Most genes have multiple alleles (different forms of the same gene)
• hair, eye, and fur color genes all have many different alleles
• multiple alleles usually exhibit some sort of incomplete dominance

8. Polygenic Traits
 The control of a trait by more
than one gene
• Skin color is controlled by at
least 6 genes
 Each gene product is
additive to the others
 The hallmark of a polygenic
trait's phenotype expression
is:
• A bell curve distribution
• A continuous distribution

9. The Human Genome Project
 In the 1950's, scientists
were first able to view a
set of human
chromosomes
 In 2003, scientists
finished mapping the
human genome
 Now every gene of
each human
chromosome is know
by location and trait

10. Human Karyotype: 23 homologous
pairs

11. Sex Chromosomes
 The X and Y chromosomes determines gender
X + Y = BOY X + X = GIRL
 The mother always donates an X chromosome.
Why?
 The father gives either an X (female) or a Y (male).

12. Sex-Linked Recessive Inheritance
 The pattern of
inheritance still follows
Mendel's predictions
 Genes found on the
X chromosome:
• Hemophilia
• Color blindness
 Males are more often
affected than females
because they inherit
only one X chromosome

13. Pedigree
 Pedigrees help track
the appearance of
one trait (or disease)
• Very useful for
determining the
type of inheritance
Does the whirling trait
appear to be sex-linked?
Are there multiple alleles for
the whirling trait?
Is it recessive or dominant?

15. Multiple Alleles

16. Autosomal Dominant Inheritance
 Genes on non-sex chromosomes are autosomes
• Huntington’s disease is an autosomal dominant trait
• It only take one copy of the Huntington gene to have the disease
 Some individuals in every generation are affected
regardless of gender
This pedigree
shows the affected
individuals of each
generation as a
black circle or square

17. Autosomal Recessive

18. Environmental Influences
 Genes are often influenced by
environmental factors
• leaf & stem size is dictated by genes, but
also affected by sunlight
• black fur color genes can be "turned on"
by changes in temperature
• conditions such as baldness can be
triggered by hormones (internal environment)
• both men and women
inherit baldness genes,
but the gene is only expressed
when exposed to high levels of
testosterone

19. Different levels of hormones affect the thickness and length of
horns in bighorn sheep, even though their genotype is identical.
Diet, exercise, and other environmental factors have been
proven to influence the expression of genes causing
heart disease, diabetes and other serious illnesses.
Exposure to chemicals during
pregnancy and early infancy can
trigger severe genetic abnormalities.

20. Abnormal Chromosome Number
 many miscarriages  this zygote has 3
copies of a
are the result of chromosome instead
extra or missing of 2
chromosomes due  instead of a
to nondisjunction homologous pair,
there is a trisomy

21. Trisomy 13 - also known as Patau's
Syndrome
An individual with full
trisomy 13 at age 7 years
(survival beyond the first
year is uncommon).
He is deaf and legally blind

22. Trisomy 21 - (Down Syndrome)