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Genetics and Heredity Part II

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Genetics and Heredity Part II. Is the study of genetics and heredity really as simple as 2 alleles and a Punnett square?. Unfortunately, NO. Darn . . . The following concepts make genetics more interesting and also more complicated:

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is the study of genetics and heredity really as simple as 2 alleles and a punnett square
Is the study of genetics and heredity really as simple as 2 alleles and a Punnett square?
slide3

Unfortunately,

NO.

Darn . . .

slide4
The following concepts make genetics more interesting and also more complicated:

- incomplete dominance

- multiple alleles

- polygenic inheritance

- environmental factors

- chromosome disorders

- sex-linked disorders

incomplete dominance
Incomplete Dominance

Incomplete dominance occurs when the offspring of 2 homozygous parents show an intermediate phenotype. (#6)

slide6

+

RED WHITE PINK (RR) (WW) (RW)

slide7

Red and white are equally dominant colors

first generation

Second generation: red and white reappear

slide8

curly

+

straight

Type of Hair

wavy

multiple alleles
Multiple Alleles

Many traits are controlled by multiple alleles. They produce 3 or more phenotypes.

slide10

Ex: blood types

3 alleles for blood

A, B, O

produce

4 blood types:

A, AB, B, O

polygenic inheritance
Polygenic Inheritance

Polygenic inheritance occurs when a group of genes work together to produce one trait. #9

slide12

As a result, many phenotypes are produced.

These 3 gene pairs work together to determine one trait.

slide14

Environmental Factors

Your environment may help determine which traits are expressed.

slide15

Ex: Your diet, exposure to chemicals or sunlight, and temperature can affect genetics.

chromosome disorders
Chromosome Disorders

Every species has a specific # of chromosomes.

Humans have 46 chromosomes or 23pairs.

slide17

Human Chromosomes

Pair #23 determines gender:

XX = girl

XY = boy.

slide18

Sometimes an error occurs during meiosis and a gamete (egg or sperm) has too many or too few chromosomes.

# of chromosomes ≠ 23

a zygote formed with one of these defective gametes usually dies
A zygote formed with one of these defective gametes usually dies.

If the zygote survives, the baby will be born with a disorder or disability.

examples of chromosome disorders
Examples of Chromosome Disorders

Down’s Syndrome: 3 copies of chromosome #21; short stature, oversized heart, learning disabilities

(#10)

slide21

Turner syndrome: only affects girls; are missing part or all of one X chromosome; neck webbing, short, infertile, severe heart and kidney problems (#13)

slide22

Autism:brain disorder; repetitive movements, delays in speech, learning, and socialization

Marfan’s Syndrome: affects connective tissue; thin body, narrow face, long limbs

(#13)

slide23

This girl is missing part of her 18th chromosome.

This boy is missing part of the 11thchromosome. (Jacobsen’s Syndrome) (#13)

slide24

Sex-Linked Disorders

Some conditions are passed only on the 23rd or the X or Y chromosome.

Since these are our sexcells, the disorders are sex-linked.

slide25

All eggs carry the X chromosome. The sperm determines the gender of a child.

Females: XX

Males: XY

X

X

Y

It’s a BOY!!

It’s a GIRL!!

if a disorder is carried on the x chromosome both boys and girls can inherit it 12
If a disorder is carried on the X chromosome, both boys and girls can inherit it. (#12)

Males:XY Females:XX

If a disorder is carried on the Y chromosome, only boys can inherit it.

slide27

Punnett square for a sex-linked disorder that’s carried on the X chromosome.

Mother does not have the disorder, but carries and passes on the gene for it.

Mother (carrier)

examples of sex linked disorders
Examples of Sex-Linked Disorders

(#14)

Baldness

Colorblindness

slide29

Duchenne Muscular Dystrophy

(#14)

Calico (cats’ fur)

slide30

Hemophilia

This hemophilia patient received only one injection (shot).

The body reacted with severe bleeding under the skin. (bruising)

(#14)

pedigrees
Pedigrees

A pedigree is a chart used to trace genetic traits throughout a family’s history.

slide32

A pedigree is very useful when trying to find the pattern of inheritance of a genetic disorder.

(colorblindness, baldness, hemophilia)

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