483 Lecture Notes - Lecture 6: Model Organism, Meiosis, Thymine

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peachtoad279

5 Jun 2018

School

University of Canberra

Department

University of Canberra

Course

483

Professor

katie cohan

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LECTURE 6 Introduction to genetics

Mendel in a “pea shell.”

• Mendel studied inheritance in peas • Crossed true-breeding plants, look at several traits

• Law of segregation –2 alleles, one from each parent –Homozygous or heterozygous –

Dominant or recessive alleles

• Law of independent assortment –Alleles from different genes assort independently

two alleles in diploids control modern genetics Traits

• Alleles occur on homologous chromosomes at a specific location (locus)

autosomes & allosomes

• So far we have talked about genes on the autosomes • What happens when

is located on

chromosomes (allosomes)?

• Sex‐linkage was not observed in Mendel’s experiments –Traits studied were not sex‐linked

• Sex‐linkage is not consistent with Mendel’s principles of inheritance –Genes on sex

chromosomes (X and Y) are inherited differently in males and females

sex‐linked genes

• Sex‐linked genes were first observed in Drosophila melanogaster by T.H. Morgan.

• White‐eye (w) is a recessive trait in Drosophila. However, the white‐eye phenotype was not

expressed in the expected proportions in male flies.

genes on the x‐chromosome A few examples:

• A gene for a blood clotting protein – recessive condition causes hemophilia

• A gene for a muscle protein –recessive condition causes Duchenne muscular dystrophy

• A gene for an eye pigment protein – recessive condition causes colour blindness

genes on the x‐chromosome Recessive X‐linked traits are more common in males

female XA XA = no disease XA Xa = no disease, carrier Xa Xa = disease male

XA Y = no disease Xa Y = disease

XA = dominant allele Xa = recessive allele

The most common X‐linked disorder in humans

female XA XA = homozygous standard XA Xa = heterozygous carrier Xa Xa = homozygous

colourblind

XA Y = hemizygous normal Xa Y = hemizygous colourblind

genes on the x‐chromosome red‐green colour blindness

Ishihara Colour Test See 74: normal colour vision

See 21: then may have dichromacy or anomalous trichromacy.

See no number at all: may suffer achromatopsia: complete blindness to colour.

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Document Summary

Mendel in a pea shell. : mendel studied inheritance in peas crossed true-breeding plants, look at several traits, law of segregation 2 alleles, one from each parent homozygous or heterozygous . Morgan: white eye (w) is a recessive trait in drosophila. However, the white eye phenotype was not genes on the x chromosome a few examples: genes on the x chromosome recessive x linked traits are more common in males. The most common x linked disorder in humans genes on the x chromosome red green colour blindness female xa xa = no disease xa xa = no disease, carrier xa xa = disease male. Xa y = no disease xa y = disease. Xa = dominant allele xa = recessive allele female xa xa = homozygous standard xa xa = heterozygous carrier xa xa = homozygous colourblind. Xa y = hemizygous normal xa y = hemizygous colourblind. Ishihara colour test see 74: normal colour vision.

Related Questions

If an organismâs diploid chromosome number is 18, how many different possible combinations of homologous chromosomes lining up during meiosis exist for the eggs or sperm produced by that organism?

	A.	512
	B.	9
	C.	18
	D.	128
	E.	36

At the end of metaphase I, _______________ separate.

	A.	sister chromatids
	B.	germ cells
	C.	homologous chromosomes
	D.	haploid chromatids
	E.	centrioles

Mendel observed that dominant traits

	A.	are seen in all of the F1 hybrid pea plants in his experiments.
	B.	are expressed in all plants.
	C.	were absent in the F1 generation of pea plants that he used in his experiments.
	D.	were the only traits seen in the F2 generation of pea plants in his experiments.
	E.	are only expressed in hybrids.

Cytokinesis in plant cells differs from cytokinesis in animal cells because

	A.	there is no difference.
	B.	in plant cells, the cell plate must also divide into two parts.
	C.	the contractile protein, actin, is important only in plant cells.
	D.	plant cells have a rigid cell wall.
	E.	a contractile ring forms only in plant cells.

Sickle cell anemia is an example of what type of inheritance?

	A.	complete dominance
	B.	incomplete dominance
	C.	codominance
	D.	multiple alleles
	E.	recessive dominance

Which of the following statements is true:

	A.	The dominant allele is masked in homozygous dominant individuals.
	B.	With recessive genetic disorders, if both parents are carriers, the offspring will all be affected.
	C.	In carriers, the recessive allele causes an intermediate phenotype.
	D.	In recessive genetic disorders, the mother and/or father of an affected individual must also be affected.
	E.	With dominant genetic disorders, the mother and/or father of an affected individual must also be affected.

Skin cancers typically develop in the

	A.	upper layers of the epidermis.
	B.	lower layers of the dermis.
	C.	subcutaneous layer.
	D.	lower layers of the epidermis.
	E.	upper layers of the dermis.

Duchenne muscular dystrophy (MD) is inherited from an X-linked recessive allele. What is the probability that a son with Duchenne MD inherited this disease from his biological father?

	A.	1/2
	B.	0
	C.	1/16
	D.	1/4
	E.	1/8

The genetic makeup of a particular trait in an individual is its

	A.	genotype.
	B.	heterozygosity.
	C.	phenotype.
	D.	filial.
	E.	dominance.

What structure holds the sister chromatids to the spindle fibers?

	A.	chromatin
	B.	kinetochore
	C.	MPF
	D.	centromere
	E.	cyclin

If you view a cell in which the genetic material is beginning to be visible as separate bodies, and the nucleus has disappeared from view, you may surmise that the cells is in

	A.	telophase.
	B.	anaphase.
	C.	interphase.
	D.	metaphase.
	E.	prophase.

Gregor Mendel was successful in his analysis of the genetics of pea plants because

	A.	he examined and analyzed both the F1 and F2 generations.
	B.	he studied the parental plants to determine their differences.
	C.	he decided to only look at his results in an objective manner.
	D.	he studied a trait that had a strange inheritance pattern.
	E.	pea plants have genetics different from other organisms.

Tall corn plants (T) are dominant to dwarf plants (tt). Solid green leaves (G) are dominant to leaves with a white tip (gg). A cross between two corn plants yielded the following phenotypes: 51 tall plants with a white tip on their leaves; 43 dwarf plants with solid leaves; 48 dwarf plants with white tips on their leaves; 45 tall plants with solid leaves. What are the genotypes of the parents that produced these plants?

	A.	None of the above
	B.	TtGg x Ttgg
	C.	ttGG x TTgg
	D.	TtGg x TtGg
	E.	TtGg x ttgg

In humans, a gene that has been identified as causing a type of skin cancer is the

	A.	superwoman echidna.
	B.	mutant superman.
	C.	sonic hedgehog.
	D.	mutant mole rat.
	E.	superhero aardvark.

The segregation principle states that in sexually reproducing diploid organisms the two copies of each gene

	A.	segregate from each other during meiosis.
	B.	must always be the same allele.
	C.	separate from each other during mitosis.
	D.	will both wind up in either the sperm or egg.
	E.	move together as a unit during meiosis.

In what phases is the genetic material in the cell correctly referred to as chromatids?

	A.	metaphase and telophase
	B.	anaphase and metaphase
	C.	interphase and telophase
	D.	interphase and prophase
	E.	metaphase and prophase

Consider two traits for an organism, determined by two genes, each of which is governed by at least two alleles. In the case of a dihybrid individual, the gametes formed will be of either the parental type or the recombinant type. Recombinant type gametes are formed because of

	A.	the principle of dihybrids.
	B.	multiple alleles.
	C.	heterozygosity.
	D.	incomplete dominance.
	E.	independent assortment.

An allele is

	A.	an alternate form of a gene.
	B.	always recessive.
	C.	the main factor determining a trait.
	D.	always one of a pair.
	E.	the dominant form of a gene.

After the DNA is replicated, and it condenses in prophase, two identical rods of DNA are seen. These are

	A.	spindle fibers.
	B.	kinetochores.
	C.	chromatids.
	D.	chromatin.
	E.	centromeres.

Special cells found in the gonads that give rise to gametes upon division are called

	A.	egg cells.
	B.	somatic cells.
	C.	germ cells.
	D.	stem cells.
	E.	basal cells.