Chapter Six: Classical Genetics Flashcards
Who is the father of modern genetics?
Gregor Mendel
How did Mendel study inheritance?
He bred garden peas and collected data from hundreds of plants across many generations and applied statistical analysis to his data
What 3 laws did Mendel’s work establish?
Law of dominance
Law of segregation
Law of independent assortment
What is probability?
The likelihood that a particular event will happen. It cannot predict whether it will actually occur, but if the sample is large enough it can give an average outcome
State the law of dominance
When two organisms, homozygous (pure) for two opposing traits are crossed, the offspring will be hybrid (carry two different alleles) but will only exhibit the dominant trait.
State the law of segregation
During the formation of gametes, the two traits carried by each parent separate
What is a monohybrid cross?
Cross between two organisms that are hybrid for a single trait
What are the phenotype (what it looks like) ratios from a monohybrid cross?
75% dominant trait
25% recessive trait
What is the genotype ratio for a monohybrid cross?
25% homozygous dominant
50% heterozygous
25% homozygous recessive
1:2:1
If the offspring phenotype ratio is 3:1 what were the parents?
They both were hybrid for the trait (monohybrid)
What is a test/back cross
Is a way to determine whether an individual organism showing the dominant trait is is homozygous dominant or heterozygous
How is a test cross done?
The individual is crossed with a homozygous recessive
Explain the 2 outcomes of a test cross
- If the individual was homozygous dominant all offspring will have hybrid genotype (dominant)
- If the individual was hybrid 50% or at least one of the offspring will show the recessive trait
What is a gene, and what is an allele?
Gene specifies which trait, allele specifies what form the gene takes
State the law of independent assortment
During gamete formation when 2 hybrids for 2 traits on separate chromosomes are crossed, the genes for 1 trait are not inherited along with the genes for another.
What is incomplete dominance?
It is characterised by blending but one, allele is more noticeable than the other. Unlike in Co dominance where both are expressed equally
How are alleles written incomplete dominance?
Different letters, all capitals since neither trait is dominant
What is co dominance?
When both traits are fully expressed. (the genotype has both dominant traits)
Most genes in a population often exist in 2 allelic forms. When > 2 its called:
Multiple alleles
Humans have 4 blood types. How many different alleles?
3
How are homozygous A and hybrid A written? Also state in terms of I
AA= I^A A(O)= Ai
How is blood type O written?
It is recessive
(ii)
What are characteristics controlled by many genes (by blending) called?
Polygenic
Which factor determines how alleles are inherited?
How the homologous pairs line up on the Metaphase plate during Metaphase 1 of meiosis
What is a dihybrid cross?
Cross between individuals that are hybrid for two different traits (Tt Yy × To Yy)
What are phenotype ratios for a dihybrid cross?
9:3:3:1
recall punnet square for Tt Yy
What are traits/genes carried on X chromosome called?
Sex-linked
Why is it that males suffer sex-linked conditions more than females?
If the condition is due to recessive mutation the female can express it only if she inherits 2 mutated genes, if one she’s only a carrier. If a male carries one mutated X-linked gene he will express it
2 examples of common recessive sex-linked traits are:
Color blindness
Hemophilia
In sex-linked inheritance how are daughters and sons affected from parents?
Affected (they have to express cannot be carriers, mutated X) fathers pass traits to daughters(carriers)
Fathers cannot pass it on to sons because they only pass on the Y chromosome
Carriers mothers can pass on the trait to sons (50% chance)
Daughters can be affected only if both parents have the trait (2 mutated Xs)
Apart from genetic predisposition what can alter the expression of genes?
The environment
Inheritance can be influenced by sex. What does this mean?
This means that a particular traits genotype and phenotype and differ between genders
What is a karyotype
It is a laboratory procedure that analyses the size, shape and number of chromosomes
How is a karyotype done?
Chromosomes are prepared and photographs during metaphase of mitosis
Differentiate the 2 types of the 46 chromosomes
44 autosomes (22 pairs) 2 sex chromosomes (1 pair)
What is a pedigree and how does it work?
It is a family tree uses to study how a phenotype of a trait is inherited for every member of a family. Females=circle Males=sqaure Carrier=half shaded (not often shown) Affected=full shaded
Recall autosomal dominant, autosomal recessive, sex linked dominant, sex linked recessive traits
Okay lol
What is a mutation?
Abnormalilty in the genome
What is a gene mutation?
Caused by a change in DNA sequence
What is a chromosome mutation?
A chromosome may sustain an addition or deletion, or a cell may even have a new chromosome, which results from nondisjunction
What are homologous chromosomes?
A couple ofhomologs are a set of 1 maternal and 1 paternalchromosomethat pair up duringfertilization. Homologs have the samegenesin the samelociwhere they provide points along each chromosome which enable a pair of chromosomes to align correctly before separating during meiosis
What is nondisjunction?
An error that sometimes happen during meiosis in which homologous chromosomes fail to separate
How can nondisjunction affect a zygote?
When nondisjunction happens 1 gamete received 2 homologues while the other receives none. When one of these gametes are paired with a normal gamete the zygote chromosome number is abnormal
What is an abnormal chromosome condition called?
Aneuploidy
What is a condition called when chromosome is present in triplicate?
Trisomy
An organism with cells with an extra set of chromosomes is called?
A triploid (3n)
An organism with more than 3 sets of chromosomes?
Polypoid
What is deletion?
A fragment lacking a centromere is lost during cell division
What is inversion?
A chromosomal fragment reattaches to it’s original chromosome but in the reverse orientation
Which mutations are visible under microscope
Chromosomal
What is translocation (in terms of chromosomal aberrations)
A fragment of a chromosome becomes attached to a non homologous chromosome
What is polyploidy?
Having extra sets of chromosomes
State what type of disorder Phenylketonuria is, it’s pattern of inheritance, and describe it
- genetic
- autosomal recessive
- inability to break down the amino acid phenylalanine. Intake of it in diet results in mental retardation
State what type of disorder Cystic Fibrosis is, it’s pattern of inheritance, and describe it
- genetic
- autosomal recessive
- buildup of extracellular fluid in the lungs, digestive tract etc
State what type of disorder Tay-Sachs disease is, it’s pattern of inheritance, and describe it
- genetic
- autosomal recessive
- onset in early life, caused by lack of enzyme to break down lipids essential for normal brain function, seizures blindness and early death
State what type of disorder Huntingtons disease is, it’s pattern of inheritance, and describe it
- genetic
- autosomal dominant
- onset in middle age, disease of the nervous system, certain early death
State what type of disorder Hemophilia is, it’s pattern of inheritance, and describe it
- genetic
- sex-linked recessive
- caused by the absence of 1/more proteins necessary for normal blood clotting
State what type of disorder Color blindness is, it’s pattern of inheritance, and describe it
- genetic
- sex-linked recessive
- being red-green colourblind is rarely more than inconvenience
State what type of disorder Downs syndrome is, it’s pattern of inheritance, and describe it
- chromosomal
- 47 chromosomes with trisomy-21 = an extra #21 chromosome
- characteristic facial features, mental retardation, prone to developing Alzheimer’s and leukaemia
State what type of disorder Klinefelters syndrome is, it’s pattern of inheritance, and describe it
- chromosomal
- XXY 47 chromosomes = male with extra X chromosome
- male genitals, but testes are abnormally small and men are sterile
What are the genotypic ratios for the monohybrid cross?
1 Homozygous dominant: 2 Hybrid: 1 Homozygous recessive
What are the phenotypic ratios for the monohybrid cross?
3 dominant: 1 recessive
