Lecture 07 Flashcards Preview

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Flashcards in Lecture 07 Deck (27):
1

Sex-limited traits

(autosomal or x-linked) traits that affect a structure or function occurring only in one sex

ex: beard growth & milk production

2

sex-influenced traits

traits in which the phenotype expressed by a heterozygote is influenced by sex

allele is dominant in sone sex but recessive in the other

ex: heterozygous male is bald, but a heterozygous female is not

3

what the phenotype in sex-influenced traits expressed by?

A heterozygote

4

The inactivated x chromosome

barr body

5

X inactivation

females have two alleles but males have only one x chromosome gene

in mammals, x inactivation balances this inequality and one x chromosome is randomly inativated in each cell

6

When does x inactivation occur

early in prenatal development

7

What is x inactivation an example of?

epigenetic change - an inherited change that does not alter the DNA base sequence

the XIST gene encodes an RNA that binds to and inactivates the x chromosome

8

Manifesting heterozygote

female that expresses the phenotype corresponding to an X-linked gene

9

genomic imprinting

the phenotype of an individual differs depending on the gene's parental origin

10

How are genes imprinted?

by an epigenetic event: DNA methylation
-methyl (CH3) groups bind to DNA and suppress gene expression in a pattern determined by the parent's sex

11

Importance of genomic imprinting

-Function plays a role in development
-explains incomplete penetrance
-two opposite sex produces a healthy embryo (male genome controls placenta development and female genome controls embryo development)

12

When are (genomic) imprints erased and what happens next?

They are erased during meiosis and then reinstituted according to the sex of the individual

13

What are the two syndromes that result from a small deletion in chromosome 15?

1) Prader-Willi syndrome - deletion inherited from father
2) Angelman syndrome - deletion inherited from mother

the two syndromes may also result form uniparental disomy

14

How do nucleotide join

via a covalent bonddbetween the 5' phosphate of one and the 3' hydroxyl of another
-this creates a continuous phosphate backbone

15

What do two aligned polynucleotide chains form?

A double helix
-hydrogen bonds forming between complementary bases holding two strands together

16

What direction does the double-helix run?

One strand runs a 5' to 3' direction and the other strand runs in a 3' to 5' direction

17

Histones

proteins that is coiled with DNA, forming a bead-on-a-string like struction, called the nucleosome, which winds tigher to form chromatin

-

18

When does DNA replication occur?

During the S phase of the cell cycle, prior to cell division
-replicates about 50 bases/sec

19

Replication fork

a site where DNA is locally opened

20

Enzymes in DNA replication

helicase
binding proteins
primase
DNA polymerase
ligase

21

How much protein-encoding genes does the human genome contain?

~20,325 protein-encoding genes (this only represents a small part of the genome)

22

What does much of the human genome control?

protein synthesis - including the time, speed, and location

23

Gene expression - difference between transcription and translation

transcription - production of mRNA

translation - production of protein using mRNA, tRNA, and rRNA

24

What type of enzyme does transcription require?

RNA polymerase

25

Transcription

RNA is synthesized from one strand, called the template strand

the complementary strand is called the coding strand of DNA

26

Two types of nucleic acids

RNA & DNA

27

Types of RNA

1) mRNA (500-4,500+ bases long) - encodes amino acid sequence
2) rRNA (100-3,000 bases long) - associates with proteins to form ribosomes, which structurally support and catalyze protein synthesis
3) tRNA (75-80) - transports specific amino acids to the ribosome for protein synthesis