Download Genetics - Bakersfield College

BIOLOGY 11
Mrs. Garrison
MENDELIAN GENETICS
GENETICS -- science of how inherited traits are passed from parent child
Each chromosome contains many different genes
gene -
allele -
Eggs and sperm carry only one set of chromosomes
genotype -
phenotype –
dominant allele –
recessive allele –
First person to work out idea of dominant and recessive traits was Gregor Mendel
purple flowers x white flowers

F1 all purple flowers
F1 x F1
1

¾ purple flowers
¼ white flowers
F2
(ratios approx.)
heterozygous
homozygous
NON-MENDELIAN GENETICS
Since Mendel’s time, we’ve found many traits which aren’t inherited in such
simple fashion:
polygenic inheritance - more than one gene (locus) controls the trait
multiple alleles - more than 2 alleles possible in whole population
incomplete dominance - heterozygote looks different than either
homozygote.
codominance - 2 different alleles do not show simple dominant/recessive
relationship; heterozygote shows both traits
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sex-linked traits - carried on the sex chromosomes (X, unless told diff.)
X chromosome is larger than Y chromosome
has many more genes (incl. all genes nec. for survival)
males only get one copy of these genes
Y chromosome has genes to determine “maleness”
GENETICS APPLICATIONS
GENETIC COUNSELING - look at family history to determine if individual has a
greater than average risk of carrying a certain allele, and what the risk to their
children would be. (THIS TYPE OF COUNSELING REQUIRES AN EXTENSIVE
KNOWLEDGE OF GENETICS, AND SHOULD BE DONE BY EXPERTS!)
amniocentesis -
karyotype -
TYPES OF DISORDERS
AUTOSOMAL DOMINANT DISORDERS- single gene (although individual
has 2 of that gene), dominant allele
AUTOSOMAL RECESSIVE DISORDERS - single gene, recessive allele
cystic fibrosis - 1 in 2000 births (1 in 20 adults are carriers)
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PKU
sickle cell anemia
albinism
Tay Sachs
SEX-LINKED DISORDERS - usually on X chromosome
red-green colorblindness
hemophilia (2 types)
Duchenne’s muscular dystrophy
cleft palate
night blindness
severe combined immunodeficiency disease (SCID)
CHROMOSOMAL ABERRATIONS - problems w/all or part of a chromsome
(broken, extra, missing chromosomes); often due to non-disjunction during
meiosis.
Down syndrome - trisomy 21; increases w/age of mother
1 in 3000 for mothers under 30 yrs.
1 in 9 for mothers over 48 yrs.
Turner’s syndrome - only one X, no second sex chromosome
1 in 2000 female births
phenotypic female, sterile
short stature, some mental impairment (not much)
Klinefelter’s sysndrome - two or more X, one Y
1 in 1000 male births
phenotypic male, sterile
tall, slender, enlarged breasts, underdev. genitalia,
sparse body hair
Cri du chat (cat cry syndrome) - missing part of chromosome 5
deletion - occurs in 1 in 50,000 births
small head, wide-spaced eyes, cry sounds like kitten
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