genetics since mendel
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Genetics Since Mendel. Unit 9 – Lesson 2 Notes. Modern Genetics. We know about dominant and recessive genes, now we are going to learn about other types of genetic traits, such as Incomplete dominance Multiple alleles Polygenic Inheritance Mutations. Incomplete Dominance. - PowerPoint PPT PresentationTRANSCRIPT
Genetics Since MendelUnit 9 – Lesson 2 Notes
Modern Genetics• We know about dominant and recessive
genes, now we are going to learn about other types of genetic traits, such as
– Incomplete dominance– Multiple alleles– Polygenic Inheritance– Mutations
Incomplete Dominance
• Neither allele for a trait is dominant.
• The phenotype produced is intermediate between the two homozygous parents.
Multiple Alleles• More than two alleles are multiple alleles.
• Traits controlled by multiple alleles produce more than three phenotypes.
Multiple AllelesThere are 3 alleles for the gene that determines blood type. (Remember: You have just 2 of the 3 in your genotype --- 1 from mom & 1 from dad).
Notice that, according to the symbols used in the table above, that the allele for "O" (i) is recessive to the alleles for "A" & "B".
ALLELE IA IB i
CODES FOR Type "A" Blood Type "B" Blood Type "O" Blood
GENOTYPES IAIA IAi
RESULTING PHENOTYPES Type A Type A
IBIB IBi
Type B Type B
IAIB Type AB
ii Type O
Polygenic Inheritance• A group of gene pairs acts together to
produce a trait, which creates more variety in phenotypes.
• Many human traits are controlled by polygenic inheritance, such as hair and eye color.
Polygenic Inheritance Example
Mutations• Mutations – genes that are
altered or copied incorrectly.
– A mutation can be harmful, beneficial, or have no effect.
– Chromosome disorders – caused by more or fewer chromosomes than normal.
Mutations– Down syndrome – caused
by an extra copy of chromosome 21.
Recessive Genetic Disorders• Both parents have a recessive allele responsible
for the disorder and pass it on to their child.
• Because the parents are heterozygous, they don’t show any symptoms.
PP Pp
Pp pp
P
P
p
p
Disorder Expressed
Recessive Genetic Disorders Examples
• Homozygous recessive disorders.
– PKU– Cystic Fibrosis– Sickle-Cell Anemia
Other Genetic Disorders• Genes that determine the sex of an organism are XX in
females and XY in males.
• Females produce eggs with an X chromosome only. Males produce sperm with either an X or Y chromosome.
EGGSXX
X
X
X
SPERMS
XX
YY
Y
Other Genetic DisordersDisorders
– Turners Syndrome XO
– Triple X Syndrome XXX
– Klinefelter syndrome XXY
– XYY XYY
Sex-linked Disorders
• An allele inherited on an X or Y chromosome is a sex-linked gene.
• Color blindness is a sex-linked disorder caused by a recessive allele on the X chromosome.
Pedigree• A pedigree follows a trait through generations of a
family.
– Carriers of trait are half shaded.– People with trait are fully shaded.– Squares show males.– Circles show females.
Orange Shows the Trait
Who carries the gene? M or F
How many people are colorblind?