6.1.3: Genetic control of body plan development Flashcards Preview

Biology A2: 6.1 > 6.1.3: Genetic control of body plan development > Flashcards

Flashcards in 6.1.3: Genetic control of body plan development Deck (38):
1

What is the large large and ancient family of genes, the homeotic genes, involved in?

The homeotic genes, are involved in controlling the anatomical development, or morphogenesis, of an organism, so that all structures develop in the correct location, according to the body plan.

2

Several of these genes contain homeobox sequences What are they sometimes called?

They are sometimes called homeobox genes.

3

How long is each homeobox sequence and what does it encode?

Each homeobox sequence is a stretch of 180 DNA base pairs (excluding introns), encoding 60-amino acid sequence, called the homeodomain sequence, within a protein.

4

What does the homeodomain sequence do?

-The homeodomain sequence can fold into a particular shape and bind to DNA, regulating the transcription of adjacent genes.
-These proteins are transcription factors and act within the cell nucleus.

5

What is the shape that these homeodomain-containing proteins fold into called?

- H-T-H
-It consists of two alpha-helices (H). connected by one turn (T).

6

What does a part of the homeodomain of the amino acid sequence recognise?

-The TAAT sequence of the enhancer region (a region that initiates or enhances transcription) of a gene to be transcribed.

7

In 1984, what did scientists working in a team headed by Walter J. McGinnis demonstrate?

-That the homeobox sequence first identified in 1983 within the homeotic genes of the fruit fly, Dorsophila melanogaster, also exist within a mouse.
-Moreover, the base sequence in these homeobox sequences were very similar in both species.
-This informed scientists that these gene sequences are crucial for the regulation of development and differentiation in organisms.

8

In 1984, what did Edward de Robertis discover and what did this discovery lead to?

-A subset of homeobox genes, Hox genes, in the African clawed frog, Xenopus.
-This discovery has led to a new branch of biology called evolutionary development or 'evo-devo'

9

Where are Hox and homeobox genes found?

-Hox genes are found only in animals.
-Homeobox genes are found in animals, plants and fungi.

10

Molecular evidence indicates that homeobox genes are present in Cnidaria, what does this mean?

-This means that these genes arose before the Paleozoic era which began 514 million years ago.
-This is before bilaterally symmetrical organisms evolved.

11

Molecular evidence indicates that homeobox genes are present in Cnidaria. This means that these genes arose before the Paleozoic era, which began 514 million years ago, before bilaterally symmetrical organisms evolved. What does this indicate?

-That these genes first arose in early ancestors, which gave rise to each of the types of organism, and have been conserved.
-The sequences are also similar in all organisms studied to date and that similarity extends across wide evolutionary distances.

12

What do the Hox genes do?

-They regulate the development of embryos along the anterior-posterior (head-tail) axis.
-They control which body parts grow where.

13

What will happen if Hox genes are mutated?

-Abnormalities can occur such as antennae on the head of Dorsophila developing as legs.
-Or, mammalian eyes developing as limbs.

14

How are Hox genes arranged?

Hox genes are arranged in clusters and each cluster may contain up to 10 genes.

15

How many Hox clusters do tetrapods have?

-In tetrapods(four-limbed vertebrates) including mammals and therefore humans, there are four clusters.
-At some stage during evolution, the Hox clusters have been duplicated.

16

In early embryonic development, Hox genes are active. How are they expressed?

In order along the anterior-posterior axis of the developing embryo.

17

What is the phenomenon known as colinearity?

The sequential and temporal (in time) order of the gene expression corresponds to the sequential and temporal development of the various body parts.

18

What do Hox clusters encode?

Homeodomain proteins

19

What do homeodomain proteins do?

They act in the nucleus as transcription factors and can switch on cascades of activation of other genes to promote mitotic cell division, apoptosis, cell migration and also help to regulate the cell cycle.

20

How can a fly function properly with a chicken Hox gene inserted in its place?

Because Hox genes are similar across different classes of animals.

21

How are Hox genes regulated.

-By other genes called gap genes and pair-ruled genes.
-In turn, these genes are regulated maternally supplied mRNA from the egg cytoplasm.

22

Which part of the cell cycle is regulated with the help of homeobox and Hox genes?

-Mitosis.
-It ensures that each new daughter cell contains the full genome and is a clone of the parent cell.

23

What happens during cell differentiation?

Some genes in a particular type of cell are 'switched off' and not expressed.

24

What did Leonard Hayflick show in 1962?

That normal body cells divide an limited number of times (around 50 times- known as the Hayflick constant) before dying.

25

What did John Foxton Ross Kerr do in 1965?

In 1965, John Foxton Ross Kerr re-examined and researched the idea of programmed cell death, first described in 1842 by Carl Vogt.

26

In 1972, the term 'apoptosis was used for programmed cell death. How is apoptosis different from cell death due to trauma?

Cell death due to trauma involves hydrolytic enzymes.

27

There are five steps (sequence of events) during apoptosis. Describe them:
Step 1:

Enzymes break down the cytoskeleton.

28

There are five steps (sequence of events) during apoptosis. Describe them:
Step 1: Enzymes break down the cytoskeleton.
Step 2:

The cytoplasm becomes dense with tightly packed organelles.

29

There are five steps (sequence of events) during apoptosis. Describe them:
Step 2: The cytoplasm becomes dense with tightly packed organelles.
Step 3:

The cell surface membrane changes small protrusions called blebs form.

30

There are five steps (sequence of events) during apoptosis. Describe them:
Step 3: The cell surface membrane changes small protrusions called blebs form.
Step 4:

Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments.

31

There are five steps (sequence of events) during apoptosis. Describe them:
Step 4: Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments.
Step 5:

-The cell beaks down into vesicles that are ingested by phagocytic cells, so that the cell debris does not damage any other cells or tissues.
-The whole process happens quickly.

32

Many cell signals help to control apoptosis. When might these signalling molecules be released?

By cells when genes that are involved in regulating the cell and apoptosis respond to internal cell stimuli and external stimuli such as stress.

33

Which signalling molecules help to control apoptosis?

These signaling molecules include cytokines from cells of the immune system, hormones, growth factors, nitric oxide.

34

How can nitric oxide induce apoptosis?

-By making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient.
-the protons are released into the cytoplasm and bind to apoptosis inhibitor proteins.

35

Why is apoptosis an integral part of plant and animal tissue development?

Extensive proliferation of cell types is prevented by pruning through apoptosis, without the release of hydrolytic enzymes that could damage surrounding tissues.

36

During limb development, what does apoptosis cause?

During limb development, apoptosis causes the digits to separate from each other.

37

During the development of the immune system, what does apoptosis remove?

Ineffective or harmful T-lymphocytes.

38

The rate of cells dying should equal the rate of cells produced by mitosis. What happens if there is...
1) Not enough apoptosis.
2) Too much apoptosis.

1) Not enough apoptosis leads to the formation of tumors.

2) Too much apoptosis leads to cell loss and degeneration.
-cell signalling plays a crucial role in maintaining the right balance.