Chapter 11 Flashcards
What does the science of genetics explain?
1) The stability of inheritance (why both you and your parents are human)
2) Why there is genetic variation between offspring and parent
Until the late nineteenth century, how did plant and animal breeders explain the pattern of of inheritance?
By blending the concept of inhertiance which states that an offspring’s genetic makeup was intermediate to that of it’s parents
According to theories of those in the nineteenth century, if two parents of contrasting appearance produce a child, then what should that child look like?
The offspring should have intermediate appearance
Give some background information on Gregor Mendel
An Austrian monk who developed a theory of inheritance after performing a series of experiments
- He applied statistical methods as well as the laws of probability to biology
- Theory of inheritance is called a particulate because it’s based on the existence of minute particles (genes)
What plants did Mendel use with his experiments?
The garden pea
Why was the garden pea a good choice?
1) Plants were easy to cultivate and had a short generation time
2) Peas could be cross pollinated
3) Many varieties of peas were avaliable
What traits did Mendel study?
Seed shape, seed color, and flower color
How did Mendel set up his experiement (Law of Segregation related)
- Called the orignal parents the P generation
- Performed reciprocal corsses
- Observed the characteristics of plants after the monohybrid cross
What is the expected phenotypic result of a monohybrid cross?
3:1
What did Mendel conclude? (Law of Segregation)
A 3:1 ratio among the F2 offspring was possible if:
1) the F1 parents contained two separate copies of each hereditary factory (one dominant and one recessive)
2) the factors separated whent the gamets were formed and each gamete carried only one copy of each factor
3) Random fusion of all possible gametes occured upon fertilization
What does the Law of Segregation state?
- Each individual has two factors for each trait
- The factors segragate (separate) during the formation of the gametes
- Each gamete contains only one factor from each pair of factors
- Fertiliztion gives each new individual factors for each trait
What is the gene locus?
The particular location where a particular gene occurs on a homologous pair of chromosomes
Why is the dominant allele named the way it is?
Because of it’s ability to mask the expression fo the other allele
Why is the recessive allele named te way it is?
Because it is usually masked by the dominant allele
How does meiosis explain the law of segregation?
During Meiosis I, the members of bivalents (homologous chromosomes) separate. That means that the two alleles for each gene separate
When an organism has two identical alleles, what do we say that particular gene is?
Homozygous
If, at a gene locus an organism has two different alleles,what is it refered to as?
Heterozygous
What does the word genotype refer to?
The alleles an individual recieves at fertilization.
What is a phenotype?
It refers to the physical appearance of the individual
What were Mendel’s second set of crosses called?
Dihybrid crosses
What does the law of independent assortment state?
1) Each pair of factors segregates (assorts) independently of the other pairs
2) All possible combinations of factors can occur in the gametes
What does the law of independent assortment apply to?
Only alleles on different chromosomes
What is the expected phenotypic ratio of a dihybrid cross?
9:3:3:1
What does the Punnett square allow one todo?
Easily calculate the chances/prpbability of genotypes and phenotypes among the offspring
What are test crosses?
They are used to support the law of segregation. One can use these tests to tell if said gene is Heterozygous/Homozygous dominant
What is an autosome?
It is any chromosome other than a sex chromosome
If a genetic disorder is autosomal dominant, then what individuals (what alleles) will contract it/
Those that have Aa genetoype of AA
If a genetic disorder is autosomal rcessive, then what individuals will have the disease?
aa
What are some autosomal recessive disorders?
- Methemglobinemia
- Cystic Fibrosis
- Niemann-Pick Disease
What are some autosomal dominant disorders?
- Osteogenesis Imperfecta
- Hereditary Spherocytosis
When a trait is controlled by multiple alleles, how does the gene exist?
In several allelic forms
What is an example of a trait controlled by multiple alleles?
Blood
What happens during incomplete dominance?
When the heterozygote has an intermediate phenotype, between that of either homozygote
What is an example of incomplete dominance?
Four O’Clocks: When a true breeding four o’clock red flower is crossed with a true breeding white flower, one of the results is a pink flower
What is an example of incomplete dominance in humans?
Familial Hyperchloesterlemia
What is incomplete penetrance?
When the dominant allele does not lead to the dominant phenotype in a heterozygote, even when the alleles show a true dominant/recessive relationship.
When does pleiotropy occur?
When a single mutant gene affects two or more distinct and unrelated traits
What are some disorders that come from pleitropy?
Marfan syndrom, porphyria, sickle cell disease, sickle cell anemia
Polygenic inheritance occurs when?
When a trait is governed by two or more sets of alleles
What are multifactorial traits?
Traits that are controlled by polygenes subject to environmental influences
What are human examples of polygenic traits/disorders?
Eye color, cleft lip/palate, clubfoot, congenital dislocations, hip hypertension, schizophrenia, as well as allergies and cancers
What does the term X-Linked?
It is used for genes that have nothing to do with gender BUT are carried on the X chromosome
What are human x-linked disorders?
Color blindness, Muscular Dystrophy, Menkes Syndrome, Adrenoleukdystrophy, Hemophilia
