Download LE#25Genetics - Manhasset Public Schools

LE­#25­Genetics
Aim#25: How are traits passed on from parents to offspring? Essential Question: How does sexual reproduction lead to variation in offspring?
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1. Genetics:
Gregor Mendel­
"Father of Genetics"
*Who was Gregor Mendel?
the study of how traits are passed along to offspring
*Activity:
1.) Read an abbreviated history of genetic discoveries.
2.) Make a timeline to summarize the events from 1860's to 1944.
1860's: Gregor Mendel discovers "factors" that determine dominant and recessive traits
LE­#25­Genetics
Terms you need to Know:
Genotype= the genes that you possess. Represented with letters.
described as being "pure" or "hybrid"
Phenotype= the physical traits or characteristics you possess because of
your genes.
This is a descriptive term like tall, short, black hair, blue eyes.
Phenotype is determined by genes + environment!!!!!!
TT­
Alleles ­ the versions of a gene that control a trait. Always expressed as letters T or t B or b Homozygous alleles ­ two alleles that are the SAME: TT tt BB bb WW ww
tt­
Heterozygous alleles ­ two alleles that are Different: Tt Bb Ww Dominant­ if allele is present, trait will show up
Recessive­ 2 alleles must be present
What happened when Mendel crossed a pure Tall plant with a pure Short plant?
Tall
All Tall plants!
short
What happened to the short? Is it gone forever?
Tt­
Lab: Human Genetic Traits
Period 2/3
LE­#25­Genetics
Lab: Human Genetic Traits
Period 8/9
VI. Law (Principle)
of Dominance:
one allele may dominate over another allele
Tall dominates over short
T>t
Smooth dominates over wrinkled
S>s
Purple dominates over white
P>p
Inflated dominates over constricted
I>i
4. Punnett
Square:
*Punnett Square Practice:
Given: In Pea Plants, T is the dominant gene for TALL, and t is the recessive gene for short.
1. Cross a short pea plant with a pure tall pea plant.
Parents: __________ x __________
a device that allows us to determine
the possible offspring that can result from the mating of two parents.
LE­#25­Genetics
Given: In Pea Plants, T is the dominant gene for TALL, and t is the recessive gene for short.
2. Cross a hybrid Tall pea plant with a short pea plant.
Parents: __________ x __________
*Let’s say you are given a rabbit that is black, but you do not know whether it is pure black or hybrid black. How can you determine its genotype?
___________________________________________
Test Cross: To determine whether a trait is pure or hybrid, cross the organism with a pure recessive. If all the offspring exhibit the dominant trait, the original organism was __________. If even one of the offspring exhibit the recessive trait then the original parent must have been __________.
LE­#25­Genetics
VIII. Law of Segregation:
In sexual organisms, genes are separated during meiosis.
Gametes = monoploid, Zygote = diploid
Different gene combinations can occur
LE­#25­Genetics
*Are there any sex­linked genetic disorders that are carried on the Y chromosome?
Yes! Hairy ears: literally lots of hair growing out of the ears.
Who would inherit this disorder? Why?_________________________________________________________
Why do you think there are more genetic disorders on the X chromosome than the Y?_____________________
_________________________________________________________________________________________
XI. Law of Incomplete Dominance (blending):
How did this happen?
RR x WW
XII. Codominance:
LE­#25­Genetics
8. Multiple Alleles:
a. Blood types also show multiple alleles!
b. More than 2 alleles for a trait
ex. A, B, O
XIV. Law of Independent
Assortment:
alleles are distributed randomly during gamete formation (genes on separate chromosomes sort independently during meiosis)
Ex. ­Tall and Green are both dominant traits: T and G
­short and yellow are both recessive traits: t and g
The complete genotype of an individual might be TTGG, ttgg, or TtGg. When filling in the punnett square, you use two genes over each box. Each filled in box will have four genes. (dihybrid cross)
LE­#25­Genetics
*Exception: Gene Linkage
Ex.
Red Hair and freckles
Brown Hair brown eyes
XV. Pedigrees:
diagram that traces the inheritance of a trait through several generations
LE­#25­Genetics
Pedigree Practice:
XVI. Genetic a. Recessive Disorders:
Disorders:
Carrier­
Disorder
Occurrence in the U.S.
Cause
Effect
Cystic Fibrosis 1 in 3500
membrane protein gene defective
Albinism 1 in 17,000
no color in skin, eyes, don't produce normal hair
susceptible to UV
melanin
vision problems
Tay­Sachs
1 in 2500
buildup of fat deposits absence of enzyme to in brain
break down fats
mental disabilities excess mucus
digestive and respiratory failure
b. Dominant Disorders:
Disorder Occurrence in the U.S. Cause Effect Huntington's Disease 1 in 10,000 defective neurological function
decline of mental and neurological functions
ability to move Achondroplasia 1 in 25,000 bone growth is abnormal
short arms and legs
large head (common form of dwarfism)
LE­#25­Genetics
LE­#25­Genetics