Biology Sections 14.1 & 14.2

What is sickle cell disease?

- a disorder caused by ONE defective allele for beta-globin which carries oxygen in red blood cells. - people heterozygous for SCD are generally healthy because they have some normal hemoglobin in their red blood cells - shape of the cells gives the disease its name

What does the inheritance pattern of X-linked recessive traits look like?

- affected daughter --> check father - if all sons of affected mom have disease, it's also X-linked - for females: XaXa to show trait - for males: XaY

Genes found on the Y chromosome...

- are only in males - inherited from father to son

There have been no reports of babies being born without an X chromosome. What does this indicate?

- chromosome contains genes that are vital for life

What are sex chromosomes?

- chromosomes that determine gender female: two x chromosomes male: 1 x chromosome and 1 y chromosome

What is a Pedigree?

- family record that shows inheritance of a trait over several generations - you can use them to infer genotypes based on a pedigree you can determine if an allele is dominant or recessive, autosomal or sex-linked See picture on p.396

Genes found on the X chromosome...

- found in both sexes - in order for a recessive allele to be expressed in females, it must be present in 2 copies - one on each X chromosome --> recessive alleles tend to be much more common in males

What are sex-linked genes?

- genes located on a sex chromosome (X or Y) Ex. Colorblindness is found more in males because its determined by the x chromosome, and it's recessive

What does the inheritance pattern of autosomal dominant look like?

- need at least one dominant allele to show trait (Aa or AA) - affected individual has at least one affected parent - occurs in both males and females

What does the inheritance pattern of autosomal recessive look like?

- trait is recessive - must be aa to show trait (Aa would be a carrier) - only expressed if BOTH parents have the gene and pass them to their offspring - can affect both male and female

How many chromosomes are shown in a human karyotype?

46

What percentage of sperm cells have an X chromosome?

50%

What are the Blood type rules?

IA and IB are codominant - if a person has both, they will be AB "i" is recessive - people with IAi will be A, and those with IBi will be B ii = Blood type O

If just one X chromosome is enough for males, how does the cell adjust to the extra X chromosome in females?

Mary Lyon found that, in female cells, genes in one of the X chromosomes are randomly switched off, forming a dense region in the nucleus called a Barr body Ex. female cats have three colors (spots happen because one X chromosome in one part of the body is turned off while it may be on in others)

What is a Karyotpe?

a picture that show complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size See p. 392

In the case of blood type, the alleles for human genes display ______________ inheritance

codominant Look at chart on p.394

What is Trisomy?

if two copies of a chromosome don't separate, offspring will have three copies ex. nondisjunction of chromosome 21 leads to Down's syndrome, usually giving those with this a total of 47 chromosomes

The recessive phenotype of a sex-linked genetic disorder tends to be more common in ________.

males

Because the X and Y chromosomes determine sex, the genes located on them show a pattern of inheritance called _____.

sex-linkage

What are autosomes?

the 44 chromosomes of the 46 in a human cell besides the 2 sex chromosomes

What is Nondisjunction?

when homologous chromosomes fail to separate during meiosis I OR meiosis II - most common error in meiosis produces gametes with an extra copy of some genes