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7.1 Chromosomes and Phenotype

!  Sec 7.1 Pg 200-203

•  SC.912.L.16.2 Discuss observed inheritance patterns caused by various modes of inheritance, including dominant, recessive, codominant, sex-linked, polygenic, and multiple alleles.

•  Students will identify, analyze, and/or predict inheritance patterns caused by various modes of inheritance.

7.1 Chromosomes and Phenotype

!  Factors that affect phenotype

•  Location on a chromosome •  Gene expression (Is the gene an autosome or sex

chromosome?)

Sex chromosomes 2 pairs (each parent) Genes with different alleles

Autosomes Most genes are autosomes Causes human genetic disorders

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7.1 Chromosomes and Phenotype

•  Caused by recessive alleles (autosomes) •  2 copies of the recessive allele must be present

to have the disorder •  Occur in offspring with heterozygous parents •  Ex cystic fibrosis

Genetic Disorders

Dominant trait (masks disease causing trait) = Normal Recessive = Disease

7.1 Chromosomes and Phenotype

!  Cystic Fibrosis

•  Cystic fibrosis, or CF, is an inherited disease of the secretory glands (make mucus and sweat)

•  two faulty genes for the disease -- one from each parent.

•  mainly affects the lungs, pancreas, liver, intestines, sinuses, and sex organs.

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7.1 Chromosomes and Phenotype

!  Cystic Fibrosis Punnett Square

7.1 Chromosomes and Phenotype

!  Disorders caused by dominant alleles are uncommon

(dominant)

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7.1 Chromosomes and Phenotype

•  Dominant Allele disorder •  Damages the nervous

system •  affects muscle coordination

and leads to cognitive decline.

•  Disorders caused by dominant alleles are uncommon

Huntington’s Disease

7.1 Chromosomes and Phenotype

!  Sex-Linked Genes

•  Traits with genes on the X or Y chromosome •  Need 2 copies of the gene to affect trait •  Found on X chromosome due to large size •  Common in Males (only 1 X chromosome)

XA = NORMAL Xa = BAD

X Chromosome LARGER Has more influence on phenotype Has more genes = affects more traits

Y Chromosome Smaller Less genes

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7.1 Chromosomes and Phenotype

!  Sex-Linked “Girls” Traits Females Males XAXA

Homozygous dominant

XAXA Normal

XAY Normal

XAXa

heterozygous dominant

XAXa Normal, Carrier (pass the trait to

offspring)

XaY Disease

XaXa

heterozygous recessive

XaXa Disease

7.1 Chromosomes and Phenotype

!  Types of Sex-Lined Traits!

•  Hemophilia •  Duchene Muscular Dystrophy •  Melanoma •  X-chromosome inactivation •  Color Blindness •  Turners Syndrome

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7.1 Chromosomes and Phenotype

!  Color Blindness

•  X-linked (Sex) Recessive allele

•  Common in MALES •  Unable to see all colors

7.1 Chromosomes and Phenotype

•  A hereditary blood disorder, primarily affecting males, characterized by a deficiency of the blood clotting protein known as Factor VIII that results in abnormal bleeding.

•  1st discovered by Jewish people. Known as the “royal disease” because Queen Victoria was a carrier

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7.1 Chromosomes and Phenotype

7.1 Chromosomes and Phenotype

!  Duchenne Muscular Dystrophy!

•  inherited degenerative disease of the muscles which progresses rapidly compared to other muscle wasting diseases. affects muscles causing progressive and degenerative muscle weakness.

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7.1 Chromosomes and Phenotype

!  X Chromosome Inactivation •  Occurs in girls •  Only need 1 X chromosome

to live •  X chromosome is TOSSED

1.  1 chromosome is randomly inactivated

2.  Lyonization “Mary Lyon” 3.  Inactive chromosoe

forms a Barr Body (dense area in the nucleus)

4.  Created clico pattern cats

7.1 Chromosomes and Phenotype

•  Female mammals have an XX genotype.

–  Expression of sex-linked genes is similar to autosomal genes in females.

–  X chromosome inactivation randomly “turns off” one X chromosome.

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7.1 Chromosomes and Phenotype

•  Male mammals have an XY genotype.

– All of a male’s sex-linked genes are expressed.

– Males have no second copies of sex-linked genes.