Chapter 12 - Mendels Expirements And Heredity Flashcards
What did Mendel discover before meiosis was understood?
The fundamental principles of inheritance
Today we refer to what basic understandings of what genes are as…
Classical or Mendelian genetics
What type of plants did mendel use mostly to study inheritance patterns?
Pea plants
What did Mendel demonstrate in his studies of traits?
That traits are transmitted from parents to offspring independent of other traits and in dominant and recessive patterns as discrete units (factors, genes)
What is blending inheritance?
A prevailing theory at the time of Mendel that inheritance involved blending of parental traits producing intermediate physical appearance in offspring
What is continuous variation a result of?
The action of many genes that determine a characteristic (eg human height)
What is discontinuous variation?
When traits are inherited as distinct classes like violet flowers vs white flowers (same characteristics but different traits)
The parents crossed in generation one is called what?
The parental generation or P0
The seeds produced by the parental generation were collected and grown the following season producing what? What happens with a seeding the following year after that?
The first filial generation or F1. Then allowing the F1 generation to self pollinate, collect and grow their seeds produces the F2 generation
Mendel performed crosses on seven different characteristics each with 2 constraining traits. What did he find when a true breeding violet plant was crossed with a true breeding white plant in F1 and in F2?
In F1 he found that 100 percent of the plants had violet flowers (white flower trait had completely disappeared) but when F1 was self pollinated and produced F2 there was a ratio of 3:1 of violet to white plants respectively.
What did Mendel call the traits that are unchanged in hybridizations and those that disappear?
Those that went unchanged were dominant traits, those that disappeared were called recessive traits
How does the masking of the recessive traits work? What needs to happen for it to be expressed?
There needs to be 2 recessive factors that are paired. Otherwise it will be dominant that is expressed. (This includes 1 dominant and 1 recessive, and of course 2 dominant)
Probability of 2 carriers of albinism having an albino child?
25%
Where are genes?
On chromosomes
Gene variants which exist at the same relative location on homologous chromosomes are called what?
Alleles
More than 1 gene (a pair of alleles) may code for a single trait called…
Polygenic inheritance
Observable traits expressed by an organism is called what? Vs what is an organisms underlying genetic makeup called?
Observable expressed traits are phenotypes while underlying genetic makeup is called a genotype
Organisms that have two identical alleles for that gene on their homologous chromosomes are called what? What if they were different what would they be called?
Identical would be homozygous while different would be heterozygous
Individuals that differ in only one characteristic that breed is called what?
Monohybrid cross
How can a dominant expressing individuals genotype be determined?
Crossing it with a homozygous individual, if it is a dominant homozygous individual then it will produce all dominant trait offspring
In rare cases heterozygous individuals appear to be intermediate between the two parents. What would that mean in snapdragons if there was a cross between homozygous parent with white flowers and homozygous with red flowers? What would they produce??
They would produce pink flowers, that is that the red flowers are incompletely dominant over allele for white flowers
Remember it is still NOT blending
Both alleles for the same characteristics are expressed. What is this called?
Codominance
In codomiance how is the MN blood groups shown in punnet square if they are heterozygotes, along with heterozygotes of ABO?
Heterozygotes of MN is expressed equally in both alleles as (LM, LN)
While heterozygotes for ABO is (IA, IB)
The sex chromosomes are non homologues in who?
The males ( the Y has almost negligible length)
The non sex chromosomes are called what?
Autosomes (1-22 pair in humans)
When a gene is present on the X chromosome, but not on the Y chromosome it is called what?
X-linked
What are males referred to in their sex chromosome since they have only one allele for x linked chromosomes?
Hemizygous
What would happen to the offspring if a female is homozygous for a recessive x linked trait?
They will get it 100% of the times since their fathers Y chromosome does not have the loci for that allele
Why can’t males be carriers for human sex linked disorders?
Because they only need to inherit one recessive mutant X Allele to be affected
-meanwhile females must inherit recessive X linked alleles from both parents
Rare recessive lethal alleles exist where the homozygous genotypes are lethal and the heterozygotes are normal. What usually happens to the development in these individuals?
They fail to develop past fertilization, or die in utero (miscarriage)
Rare dominant lethal alleles also exist where both homozygous and heterozygous individuals die, this allele can only be inherited if the lethality phenotype occurs when? What is the main example of this type of disease and when does onset occur?
Lethality phenotype occurs after reproductive age, it often seen in Huntington’s disease where heterozygous individuals will eventually develop the fatal disease, onset does not occur until age 40
There is a 50% chance they pass it to their offspring
What did independent assortment look at?
When 2 different characteristics relate to each other
The physical basis for the law of independant assortment lies when?
In meiosis 1 when different homologous pairs line up in random orientations on the metaphase plate
What can violate the law of independent assortment?
Linked genes, that is genes in the same chromosome. Genes need to be in different chromosomes for it to work.
How are genes located physically close to each other in the same chromosome likely to be inherited?
As a pair
When genes act antagonistically to other genes it is called…
Epistasis
Genes being masked are called what? While the genes doing the masking are called…
Masked genes are hypostatic genes, the genes that do the masking are called epistatic genes
