XII Chap 5 Inheritance & Variation Flashcards
Genetics is a branch of biology that deals with
principles of inheritance, its practices and variation of characters from parents to offspring
Define inheritance
process by which characteristics are passed from parents to progeny
Define variation
Degree by which progeny differ from parents
What is the evidence that early humans knew sexual reproduction was linked to variation
selective breeding of plants and animals (e.g. Sahiwal cows)
How early did we (humans) know that sexual reproduction was linked to variation?
Early humans (8000-1000 BC)
Who conducted hybridization experiments to determine the laws of inheritance?
Mendel
When did Mendel conduct his hybridization experiments?
1856-63
What type of plants and how many plants did Mendel use during his experiments?
14 true-breeding plants
What are the 7 pairs of traits Mendel tested?
- Stem height (tall v. short)
- Flower color (violet v. white)
- Flower position (axial v. terminal)
- Pod shape (inflated v. constricted)
- Pod color (green v. yellow)
- Seed shape (round v. wrinkled)
- Seed color (yellow v. green)
What is a true-breeding plant?
Continuous self-pollination would show stable trait inheritance and expression for several generations
What is a gene?
Unit of inheritance;
contains information to express a trait
Gene was first called a ______ by Mendel
Factor
What is an allel?
Pair of contrasting trait;
slightly different form of the same gene
What is genotype and phenotype?
Genotype = technical way of writing the gene e.g. TT or tt Phenotype = observable / descriptive characteristic
Heterozygous v. homozygous?
Hetero - dissimilar alleles (contrasting traits)
Homo - similar alleles (identical traits)
True breeding plants are heterozygous. T or F?
False
Homozygous => identical alleles
The F1 generation of a cross of a true-breeding plant will be heterozygous. True or False?
True
What is F1 represent?
Filial 1 progeny => first hybrid generation
Define monohybrid
Hybrid made from genes controlling for one/single character (flower position)
What is a monohybrid cross?
Cross between gene controlling for 1 trait e.g. pod shape
What is a Punnett Square
Diagram by British geneticist, Reginald C. Punnett;
calculates probability of all possible genotypes of offspring in a cross
What is a “test cross”?
To determine the genotype of a dominant phenotype, crossing it with recessive parent (instead of self-crossing)
What are the principles/laws of inheritance?
Law of Dominance - in dissimilar pair, one dominates the other
Law of Segregation - alleles don’t blend, they separate and gamete receives only ONE of two alleles
The law of dominance implies that only one parent’s characteristics are expressed in filial progeny 1. True or False?
True
The law of dominance implies that only one parent’s characteristics are expressed in the second generation of hybrid. True or False?
False, both are expressed
What are the phenotype and genotype ratios of the second hybrid generation?
Phenotype 3:1
Genotype 1:2:1
What are the phenotype and genotype ratios of the first hybrid generation?
Phenotype: 4:0
Genotype: 4:0
The genotype of the second hybrid generation can be expressed by which binomial equation?
(ax + by) ^2
According to the law of segregation, gamete only receives one of 2 alleles. True or False?
True
What is incomplete dominance?
An in-between state, neither dominant nor recessive gene but a blending of the two to product a 3rd phenotype
Dogflower is an example of ________________
incomplete dominance
Red (RR), Pink (Rr) and White (rr)
What are the phenotype and genotype ratios of a hybrid exhibiting incomplete domination of 1 factor?
Phenotype: 1:2:1
Genotype: 1:2:1
The genotype ratio of incomplete dominance is different than that of Mendelian monohybrid cross. T or F?
False, same
The phenotype ratio of incomplete dominance is different than that of Mendelian monohybrid cross. T or F?
True
Incomplete dominance 1:2:1
Mendelian monohybrid 3:1
What is co-dominance?
When traits of BOTH parents are observed e.g. AB blood groups
How many phenotypes and genotypes in human blood groups?
4 phenotypes
6 genotypes
What is the gene representation for blood groups in humans? What are the different alleles?
I 3 alleles: IA IB i
How does the plasma membrane of an RBC look based on ‘i’ gene?
No sugar - no protuding sugar polymers
How does the plasma membrane of an RBC look based on IA or IB gene?
Sugar polymer protruding from the plasma membrane
If a human gene has 3 or more alleles, what is the challenge in studying the variations?
Humans are diploid => they’ll possess only 2 of the 3 alleles => can only study such alleles via population studies
Occasionally one gene manifests as 2 effects or phenotypes. T or F?
True
How does one interpret dominance when a gene translates to 2 phenotypes? Give an example
Depends on the phenotype.
e.g.
Starch synthesis gene in pea seeds;
heterozygous seeds are round => dominance of B allele
heterozygous seeds are intermediate size => incomplete dominance
Dominance is an autonomous feature of a gene. T or F?
False, depends on the phenotype being examined
When 2 traits are crossed simultaneously it’s call a _________ cross
Dihybrid
What factors did Mendel study when exploring inheritance of 2 genes
Round, yellow seed
Wrinkled, green seed
What are the phenotypes and genotypes of Mendel’s dihybrid cross?
Phenotypes (16 total) 9:3:3:1
Genotypes (8 total) 1:1:1:1:2:2:2:2:4
What is the law of independent assortment?
When 2 pairs of traits combined in hybrid, segregation of 1 pair is independent of other
Who rediscovered Mendel’s experiments in 1900s?
deVries, Correns and von Tschermark
Who made the connection that both genes and chromosomes appear in pairs?
Sutton and Boveri
What is the chromosomal theory of inheritance?
Pairing and separation of a pair of chromosomes leads to segregations of a pair of factors (genes)
Who is credited with the chromosomal theory of inheritance?
Sutton and Boveri
What did Morgan & Co contribute?
Idea of linkage and recombination; law of independent assortment doesn’t apply when both genes are on the same chromosome, distance between both affects the frequency in progeny
Two genes on the same chromosome indicates more parental combinations than non-parental in subsequent generations. T or F?
True
Define linkage
Physical association of genes on same chromosome
Recombination
generation of non-parental combinations
When genes are tightly linked they have ______ recombinations. Example?
low (ie. more parental combinations);
white eyes and yellow bodies in Drosophila - 1.3% recombination in F2
When genes are ________ linked they have high recombinations
Loosely;
white eyes and miniature wing => 37.2 % recombination in Drosophila F2
Morgan’s student ________________ is credited with the concept of “genetic maps”
Alfred Sturtevant
What does it mean to “map the position” of a gene?
Use frequency of recombination as a measure of distance between 2 genes
Genetic maps is another name for _________
mapping positions of genes
Genetic maps are used in which large-scale project recently?
Human Genome Sequencing Project
What are polygenic traits? (aka polygenic inheritance)
3 or more genes have an additive effect; phenotype is on a gradient, shows influence of each gene
e.eg. human skin color, height
Polygenic inheritance takes into account genes and what other factor?
Environmental influence
What is a pleiotropic gene?
One gene, multiple phenotype;
gene effects metabolic pathway
e.g. gene that codes enzyme phenyl alanine hydroxylase, incorrect coding of which results in phenulketonuria (genetic disorder)
Henking in 1891 discovered what?
“X body”, specific nuclear structure that only 50% of sperms receive
Sex determination in insects is of type _____
XO
Eggs have additional X
Sperms may or may not
e.g. grasshopper
Grasshopper sperms which have an “X” chromosome will produce __________
Females
Grasshopper sperms which lack an “X” chromosome will produce __________
Males
Humans, mammals and some insects have _____ type sex determination
XY
Drosophila have XO type of sex determination. T or F?
False, XY (like humans)
Humans and birds exhibit male heterogamety. T or F?
Humans - male heterogamety
Birds - female heterogamety
What is male/female heterogamety?
Display pair of different sex chromosomes e.g. XY in human males, ZW in female birds
Birds and humans both have same number of chromosomes in male and females. T or F?
True
There is equal probability that an ovum will fertilize with an X-sperm or a Y-sperm. T or F?
True
Honeybees have a _______________ system of sex determination
Haplodiploid
How does sex determination work in honey bees?
Sperm + Egg = Female (queen or worker)
Unfertilized Egg = Male
Honey bees have both diploid males and haploid females. T or F?
False, diploid females and haploid males
How many chromosomes in a male v. female honeybee?
Male = 16 Female = 32
Why is it that male honeybees can neither have sons or fathers but can have grandfathers or grandsons?
Males are result of unfertilized egg => that egg has no father
Male sperms can fertilize an ovum to produce a female who may then produce an egg that is fertilized by another sperm => can be grandfathers / have grandsons
Honeybee eggs become males through process of ___________
Parthenogenesis
How do male honeybees produce sperms?
Mitosis
Define mutation
Alteration in DNA sequence / genetic material => causes change in genotype and phenotype
e.g. cancer, sickle-cell anemia
Both recombination and mutation ____________
alter DNA
What is DNA?
Helix that runs continuously from one end to another, highly coiled
__________ are chemical and physical factors responsible for mutations
Mutagens e.g. UV radiation
What is pedigree analysis?
Since crosses can’t be performed on humans, we analyze traits in several generations of family
What are the 2 categories of genetic disorders?
Mendelian
Chromosomal
What are Mendelian disorders
Alteration in a single gene
Principle of inheritance
Pedigree analysis
What are the Mendelian disorders covered in this chapter?
Color blindness Haemophilia Sickle-cell anemia Phenylketonuria Thalassemia
Mendelian disorders could be linked to a dominant or recessive gene, X-chromosome or autosome. T or F?
True
Main points about color-blindness
X-linked, recessive
defect in red/green cone of eye
affects 8% males and only 0.4% females
Daughter will be color-blind only if _________
Father is color-blind and mother is carrier (or color blind)
Main points about haemophilia
X-linked, recessive;
single protein in cascade involved in blood clotting affected => non-stop bleeding
possibility of daughter having haemophilia is rare because father being haemophilic in later stages of life is unlikely as survival rate is low
Daughter will be haemophilic only if _________
Mother is carrier and Father is haemophilic (highly unlikely due to low survival)
Queen Victoria is a famous carrier!
Main points about sickle-cell anemia
Autosome-linked, recessive;
causes RBC to be elongated, sickle-shape => not enough healthy blood cells to carry oxygen in body
Hbs Hbs (homozygous for Hb^s) are affected
Substitution of valine for glutamic acid at 6th position in beta globin chain of haemoglobin; mutation GAG to GUG
Main points about phenylketonuria
Autosome-linked, recessive;
gene that codes for enzyme phenyl alanine hydroxylase;
lacks enzyme to convert phenylalanine to tyrosine, so it converts to phenylpyruvic acid which accumulates in the brain => causes mental retardation + loss of hair + skin pigmentation
Main points about thalassemia
Autosome-linked, recessive
blood disease;
transmitted if both are unaffected carriers (or heterozygous)
Is thalassemia due to mutation or deletion of gene?
Could be either,
alpha - mutation or deletion
beta - mutation
What is alpha thalessemia?
HBA1 and HBA2 gene are closely linked on chromosome 16 of each parent. If any of the 4 genes are mutated or deleted => alpha thalessemia
The more the number of genes affected => the lesser the alpha globin molecules produced
What is beta thalassemia?
Single gene on HBB on chromosome 11, if one or both mutate
__________ is a quantitative problem of synthesizing too few globin molecules and _________ is a qualitative problem of incorrectly functioning globin molecules
Thalessemia - quantitative
Sickle-cell anemia - qualitative
What is aneuploidy?
Failure of segregation of chromatids during cell divisions => gain or loss of chromosome e.g. Down’s syndrome
What is polyploidy?
Increase in whole set of chromosomes because or failure of cytokinesis after telophase stage of cell division
e.g. often in plants
What is trisomy?
Extra or third chromosome
e.g. Down’s Syndrome
Down’s syndrome was discovered by Langdon Down in ______
1866
What is monosomy?
only 1 chromosome (where there should be 2)
e.g. Turner’s syndrome
Characteristics of Down Syndrome?
Short, flat back of head, small/round head, furrowed tongue, open mouth, palm crease,
physical, psychomotor and mental retardation
What is Klinefeller’s syndrome?
XXY => Extra copy of X chromosome, 47 karyotype
overall masculine development (tall) + breast (gynaecomastia)
What is Turner’s Syndrome?
XO => one less X => 45 karyotype;
rudimentary ovaries, short stature, underdeveloped female character
People with Turner’s syndrome and Klinefeller’s syndrome are both __________
Sterile;
have a mutation of the X chromosome
What is difference in Mendelian and Chromosomal disorders?
Mendelian - alteration of a single gene, follows principle of inheritance so can be traced by pedigree analysis
Chromosomal - absence/excess/abnormal arrangement of chromosome(s), cannot be traced
Recessive genes are only expressed in homozygous conditions. T or F?
True
Mendel’s law of independent assortment is not valid for _________
linked genes (genes on same chromosomes)
Closely linked genes are assorted together. T or F?
True
Which of these is the ultimate source of allelic variation is? Recombination Natural selection Mutation Drift
Mutation
Sickle cell anemia results from which of these? Chromosomal aberration Non disjunction of autosome A point mutation Blood transfusion reaction
A point mutation
Two alleles of a gene pair are located on ________ sites of ________ chromosomes
Homologous / heterologous
Homologous sites on homologous chromosomes
What Mendelian disorders are connected to the X-gene?
Color blindness
Haemophilia
George Mendel was born in
19th century (1800s)
Who was the first to use statistical analysis and mathematical logic to solve biology problems?
Gregor Mendel
