Download Summary - JBennett

Summary:(U4)
-genetic terms
Homework:
-read p.
-do p.
GENETICS
Genetics is the study of hereditary information with respect to its coding and method of
transmission from one generation to the next
Gene: a unit of hereditary information
-a gene is now known as pieces of DNA responsible for production of one protein
-the letter chosen to represent the gene is best if capital and small case letters are easily
distinguished
Allele: alternate form of the same gene
e.g. the gene for hair colour has brown and blonde alleles
Dominant: when two different alleles are present the one that is expressed is dominant
e.g. brown is dominant to blonde, indicated with capital letter (B)
-dominant alleles are not always the most common trait
Recessive: when two different alleles are present the one that is not expressed is recessive
e.g. blonde is recessive to brown, indicated with a lower case letter (b)
Homozygous: when an organism has two identical alleles for one gene
e.g. BB (dominant) or bb (recessive)
Heterozygous: when an organism has two different alleles for one gene
e.g. Bb (the dominant trait is expressed)
Genotype: the symbolic representation of the alleles for the trait
e.g. BB, Bb, bb
Phenotype: the physical result of the genotype
e.g. Brown, Blonde
Gametes: cells resulting from meiosis and are haploid (one set of chromosomes) e.g. sperm and
egg
Somatic cells: regular body cells and are diploid (two sets of chromosomes)
Zygote: fertilized egg, diploid because it is formed by the fusion of two haploid cells
Progeny: another term for offspring
Diploid Number: a double set of chromosomes (normal number found in somatic cells)
e.g. humans 2n# = 46, chimps 2n# = 48, fruit fly 2n# = 8
Haploid Number: a single set of chromosomes (normal number found in gametes)
e.g. humans 1n# = 23, chimps 1n# = 24, fruit fly 1n#=4
Monohybrid Cross: a mating looking at one gene and two alleles
e.g. BB X bb uses the gene for hair colour, alleles are brown and blonde
Dihybrid Cross: a mating looking at two genes and four alleles
e.g. BBRR X bbrr uses the genes for hair colour and eye colour, alleles are brown/blonde hair,
brown/blue eyes
Parental (P) Cross: a mating of any two parents
First Filial (F1)Generation: offspring of P cross
F1 cross: mating of first filial generation
(not done in humans too often...generally frowned upon because the danger of two rare
deleterious recessives combining is high in siblings)
Second Filial (F2) Generation: progeny of F1 cross
Summary:(U1)
-describe Mendel’s work
- monohybrid crosses
Homework:
-read p.
GREGOR MENDEL
Gregor Mendel was the first to study genetics scientifically
-he was a monk who worked with peas in the mid 1800’s
Why work with peas? -can be self pollinated, easy to control parental crosses (p. 155, fig. 6.4)
-grow quickly
-produce many seeds, improving statistics
-have many obvious, contrasting traits (p. 156, fig. 6.5)
Mendel’s experiments with peas led him to the following conclusions:
1. inheritance of traits was determined by genes...these genes are found in pairs (diploid)
2. one gene of each pair is in a gamete (haploid)
3. gametes unite randomly
Mendel’s Laws:
Law of Dominance:
-if two different alleles are present for one gene (heterozygous), one allele will be expressed
(dominant) and the other hidden (recessive)
Law of Segregation:
-gametes contain one gene of each pair, which segregate randomly
eg. Bb will form gametes with B and b in a 1:1 ratio
MONOHYBRID CROSS
When genetics problems arise a certain form is used to predict offspring
eg. A heterozygous (hybrid) purple flowered male pea is mated to a white flowered pea
What offspring will be produced?
This is a monohybrid cross, which involves one gene with two alleles
determine what trait is dominant:
-in a heterozygous organism, only the dominant trait is expressed
-purple must be dominant
give name of organism and gene studied:
PEAS, flower colour
write a legend showing dominant and recessive genes:
Q = purple (dominant)
q = white (recessive)
write the phenotype of the parents:
Purple male
X
White female
write the genotype of the parents:
Qq male
X
qq female
write the gametes produced by each parent:
Q q
q
q
Place gametes around a Punnett square, find offspring:
male gametes down side, female gametes along top
gametes
q
q
Q
Qq Qq
q
qq qq
Genotype ratio of F1: 1 Qq : 1 qq
Phenotype ratio of F1: 1 purple : 1 white
Summary:(U3,U7,D2)
-describe dihybrid crosses
-describe independent assortment
Homework:
-read p.
-do
DIHYBRID CROSSES
Dihybrid crosses: a genetic cross studying two genes and four alleles
eg. A heterozygous tall, green pea is mated with a short, heterozygous yellow female pea
organism/genes:
Pea: height, colour
legend:
B = tall (dominant)
b = short (recessive)
E = yellow (dominant)
e = green (recessive)
P phenotypes:
hetero. tall, green male
X
P genotypes:
Bbee
X
short, hetero. yellow female
bbEe
gametes formed:
Be Be be be
bE be bE be
Punnett square:
gametes
bE
be
bE
be
Be
BbEe Bbee BbEe Bbee
Be
BbEe Bbee BbEe Bbee
be
bbEe
bbee
bbEe
bbee
be
bbEe
bbee
bbEe
bbee
g ratio of F1:
4 BbEe: 4 bbEe: 4 Bbee: 4 bbee
or
1 BbEe: 1 bbEe: 1 Bbee: 1 bbee
p ratio of F1: 1 Tall, Yellow: 1 Short, Yellow: 1 Tall, Green: 1 Short, Green
Mendel’s law of Independent Assortment:
-one gene behaves independently of another gene during gamete formation
-this works if genes are on separate chromosomes chromosome
(different chromosome pairs separate independently during meiosis)
-this also works if the genes are far apart on the same chromosome
(genes far apart have a large number of crossovers between them during prophase I of meisosis)
-Mendel knew none of these reasons
eg. gametes formed for BbEe are BE, Be, bE, be
Cross BbEe X BbEe as practice:
p ratio of F1 should be 9 Tall, Yellow: 3 Tall, Green: 3 Short, Yellow: 1 Short, Green
Summary:(U7,D2)
-describe hazards of inbreeding
Homework:
-review p.
-do
INBREEDING
Inbreeding:
-most families have deleterious (dangerous) recessive alleles hidden in their genes by dominant
genes
-the chance of an unrelated person having this same recessive is slim
-if a person mates with a direct relative the chance of the same two deleterious recessive genes
coming together (being homozygous) in their offspring is higher than with random mating
-these recessive genes are expressed only when homozygous
-this holds true for most species
eg. dog breeding is monitored in order to prevent inbreeding (kennel clubs)
Summary:(U6)
-describe incomplete dominance/co-dominance
Homework:
-read p.
-do pg.
INCOMPLETE/PARTIAL DOMINANCE
-when heterozygous individuals are present for certain traits, the resulting phenotype is a blend of
the two alleles
-neither allele is dominant over the other
-two different letters are used for the same gene in this case
eg. a red and a white flower are crossed to make pink flowers
R = red flower
A = white flower
RA = pink flower
Red flower
RR
R R
gametes
X
X
A
White flower
AA
A A
A
R
RA RA
R
RA RA
g ratio: all RA flowers
p ratio: all pink flowers
CO-DOMINANCE
-two traits are sometimes both FULLY expressed, not blended.
eg. in blood there are two dominant alleles and one recessive allele
I = dominant, with two alleles, IA and IB
i = recessive
Phenotype Genotype
(blood type)
A
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
An AB type parent mates with an O parent
AB
X
O
IAIB
X
ii
IA IB
i i
gametes
i
i
IA
IAi IAi
IB
IBi IBi
g ratio: 1 IAi: 1 IBi
p ratio: 1 A: 1 B
-while blood type can disprove paternity, it cannot prove paternity
-any other person with the same blood type may be responsible