Genetics Notes Part 1
9.1 The Science of genetics has ancient roots
Greek: Hippocrates Hypothesis: pangenesis: pangenes from each part of the body travel to sperm or egg
Aristotle rejected his hypothesis
9.2 Experimental genetics began in abbey garden
Heredity- the passing of traits from parent to offspring
Genetics- is the science of heredity
1.
Gregor Mendel- 1860s monk who was the first to study genetics
a.
b.
c.
d.
e.
2.
Worked with pea plants, discovered how traits are passed from one generation to the next
Some traits that were studied: seed shape, seed color, flower color, height etc.
Pea plant reproduce sexually, with both sex organs in the same flower, usually self-fertilize
Mendel mated (crossed) different offspring, cross-fertilize
When he mated different types (example Short and Tall), the trait that was shown in the offspring was
called the dominant trait (all offspring =Tall)
Offspring of a parent (P generation) cross are called F1 generation, offspring of the second cross are called
the F2 generation
9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic
1. Traits
a. Dominant Traits- Form of the trait that dominates, and prevents the showing of the recessive trait
b. Recessive trait-Trait that is hidden by the dominant one
2. Genes:
a. Allele: each form of a trait (Example: eye color- blue and brown are alleles for that trait)
a. Symbols:
i. Dominant Trait is represented by a capital letter
1. Brown eyes = B
ii. Recessive Trait is represented by a lower case letter
1. Blue eyes= b
b. Each gamete (sex cell) has one allele for each gene
i. Ex: Sperm has one allele for eye color and egg has one allele for eye color
c. Three possible gene combinations
i. Homozygous dominant= two dominant alleles (BB)
ii. Homozygous recessive= two recessive alleles (bb)
iii. Heterozygous or Hybrid = one dominant and one recessive allele (Bb)
d. Genotype: Gene combination of any given trait (genes that one has (BB))
e. Phenotype: expression of that gene (Trait being expresses(Brown Eyes))
Example: Genotype: Phenotype
BB= Brown eyes
Bb= Brown eyes
bb= Blue eyes
Principle of segregation: During gamete (sex cell) formation the pair of genes responsible for each trait separates
so that each gamete receives only one allele for each trait.
Example: Monohybrid Cross: parents differ in only one characteristic. Let’s cross a homozygous brown eyes
(BB) with a homozygous blue eyes (bb)
Punnette square to predict F1 Generation:
Punnette square to predict the F2 Generation
9.5 The principle of independent assortment is revealed by tracking two characteristics at once
Example: Dihybrid Cross Parents differ in two characteristics. RRYY (yellow round) x rryy (green shrivel)
What is the genotype of all offspring or F1? ______ What is the phenotype of all offspring or F1?______
What are the four types of gene combinations that can be found in the gametes? ___ ____ ____ ____
Use a 4 box by 4 box grid to find the F2 generation.
Conclusion: Principle of independent assortment: each pair of alleles segregates independently during gamete formation
9.6 Geneticists use the testcross to determine unknown genotypes
Define Testcross:
Problem: Ms. Bell owns a purebred long haired Jack Russell Terrier named Bandit. JRTs are more valuable if they have
long hair (L) as opposed to short hair (l). Recently, the breeder Ms. Bell got her dog from has been charged with selling
dogs that are not purebred long haired terriers! Now, Ms. Bell wants to find out if the breeder charged her for a purebred
long haired dog and got a heterozygous long haired one instead! How can Ms. Bell find out if she was cheated? Create
the two possible punnette squares.
If one of the offspring to the testcross has short hair, was Ms. Bell cheated?______
9.7 Mendel’s principles reflect the rules of probability
Rule of Multiplication
DefinitionRule of Addition
DefinitionProblem: If a golden retriever Bb is crossed with a golden retriever Bb.
1.Show mathematically how to determine the probability that the offspring will be BB.
Rule Used:____ Probability BB:___
Calculations:
2.Show mathematically how to determine the probability that the offspring will be Bb.
Rule Used:____ Probability Bb:___
Calculations:
3.Show mathematically how to determine the probability that the offspring will be bb.
Rule Used:____ Probability bb:___
Calculations:
Draw the Punnette square to check your answer:
Challenge: In this cross, three genes are present: A, B and C. If one parent is AABbCC and the other parent is AaBbCc,
what is the probability that the offspring from this cross will be homozygous dominant for all three genes (AABBCC)?
9.8 Genetic Traits in humans can be tracked through family pedigrees Define the following words and draw a sample
pedigree of your family and include their genotype for a specific trait (Hint: I will never know if it is your real family)
Pedigree:
Carrier:
Drawing
9.9 Many inherited disorders in humans are controlled by a single gene Describe the following words and diseases
Recessive Disorders:
Dominant disorders:
Disorder
Recessive:
Albinism
Cystic Fibrosis
Galactosemia
PKU
Sickle Cell
Homozygous
Tay Sachs
Dominant:
Achrondroplasia
Alzheimer’s
Huntington’s
Hypercholesterolemia
Descriptions/Symptoms/Comments
Incidence
9.10 Fetal testing can spot many inherited disorders early in pregnancy Answer the following questions
1) Amniocentesis
Steps:
Why might a pregnant female choose to have this test done?
2) Chorionic villus sampling
Steps:
Advantage:
3) What are the risks of amniocentesis and CVS?
4) Describe ultrasound and fetoscopy. What is the difference?
5) What else can be analyzed to determine the health of the baby?
9.11 The relationship of genotype and phenotype is rarely simple
Detailed Description from book
9.12 Incomplete
Dominance
9.13
Codominance
9.14 Pleiotrophy
9.16 Polygenic
Examples from the book
Blood Type: Multiple alleles: a set of three or more different alleles controlling a trait
a. Each individual only gets two alleles
b. Example: Blood type is an example of multiple alleles and Co-dominance (More than one can be
dominant)
c. I A and I B are both dominant over i, but I A and I B are both expressed (Blood type AB)
d. Antigens:_____________________________________________________________________
Example: Blood type A has A antigens
e. Antibodies are______________________________________ ________________________
Example: Blood type A makes Anti-B antibodies
Blood Type
(Phenotype)
A
B
AB
O
Genotypes
Blood Type Challenge: USE PENCIL!!!!!
Information we know about the family:
John and Tom are brothers
George is blood type O
Bill’s Mother is Sally
John and Harry are blood type A
Mary is going to marry George next month
Bill and Tom are brothers
Bill is blood type AB
Tom’s blood is homozygous recessive
Mary is blood type B
Mary’s father is Harry
Mary and John are brother and sister
Antigen
Antibody
Receive from
Questions to Answer
1) What is John’s genotype?___
2) What are the chances of George’s
children being blood type O?____
3) What is Sally’s blood type?___
4) What is Sally’s genotype?___
5) What is Mary’s genotype?__
Draw the pedigree
9.17 Chromosome behavior accounts for Mendel’s Principles: Describe the following theory
The Chromosome theory of Inheritance:
Segregation:
Independent Assortment:
9.18 Genes on the same chromosome tend to be inherited together
Define linked genes:
Drawing:
9.19 Crossing over produces new combinations of alleles
Recombination frequency:
Draw Example
9.20 Geneticists use crossing over to map genes.
Describe how geneticists use crossing over to map genes.
If you have genes A B C and D on a chromosomes with the recombination frequencies A-B= 50% , A-C= 5%, B-D=10%, CD=20% , draw what the chromosome might look like.
9.21 Chromosomes determine sex in many species
Organism
Human
Grasshopper, crickets, roaches
Fish, butterfly, bird
Ants and bees
Date, spinach
Wild strawberry
Details about sex determination
Female___ Male___ Sex of offspring determined by________________
___________________________________________________________
Female___ Male___ Sex of offspring determined by________________
___________________________________________________________
Female___ Male___ Sex of offspring determined by________________
___________________________________________________________
Lack ________________, Females _____________________________
Males_____________________________________________________
System:______
System:______
Define monoecious:
Define hermaphroditic:
9.22 Sex-linked genes exhibit a unique pattern of inheritance
What is a sex linked gene?
Why are most sex linked genes found on the X?
Draw a punnette square that crosses a white eyed female fruit fly and a red eyed male fruit fly. Write the female on the
side and the male across the top of the punnette square.
What percent of the offspring will have red eyes? ____ white eyes____
What percent of the males will have red eyes? ____ white eyes____
What percent of the female will have red eyes?______ white eyes____
9.23 Sex-linked disorders affect mostly males
Describe the following disorders
1) red-green color blindness
2) Hemophilia
3) Duchene muscular dystrophy
Neither Sue nor Tom has Duchene muscular dystrophy, but their first son does. If the couple has a second child, what is
the probability that he or she will also have the disease?___ what is the percent chance that the child will be a carrier for
muscular dystrophy?____
Show the punnette square